What's going on here?

[David Dahlem]

[d]8/RP1P4/4k3/3pnp1p/8/P7/P3pPKp/8 w - - 0 1

Another position with odd evaluations. Stockfish sees a win for White, while Rybka initially likes White, then all of a sudden, score drops to 0.00. Firebird gradually drops from a winning score to 0.00, then gradually climbs again. Is this a null move issue or what?

Stockfish 1.6.3s:

26 09:57 702.049.440 1.175.716 +8.40 d7d8N+ Ke6f6 Ra7a6+ Kf6g5 Nd8f7+ Kg5h4 Ra6a4+ d5d4 Ra4xd4+ Ne5g4 Rd4xg4+ f5xg4 b7b8B h2h1Q+ Kg2xh1 e2e1Q+ Kh1g2 Qe1e4+ Kg2h2 g4g3+ Bb8xg3+ Kh4g4 f2f3+ Kg4xf3 Nf7g5+ Kf3e3 Bg3f2+ Ke3xf2 Ng5xe4+ Kf2e3 Ne4c5 Ke3d4 Nc5b3+ Kd4c4 a3a4 Kc4b4 a4a5 Kb4b5 Kh2g2 Kb5a6 Kg2g3 Ka6b5 Kg3h3 Kb5a6 Kh3h4 Ka6b5 Kh4xh5 Kb5a6 Kh5g4 Ka6b5 Kg4f3 Kb5a6 Kf3e4 Ka6b5 Ke4d5 Kb5a6 Kd5c6 Ka6a7 Nb3c5 Ka7b8 a5a6

Rybka 3:

8 00:02 210.089 88.787 +11.36 d7d8N+
9 00:04 339.173 87.484 +8.45 d7d8N+
10 00:11 1.183.074 103.783 +4.85 d7d8N+ Ke6f6 Ra7a6+ Kf6g5 Nd8f7+ Ne5xf7 Ra6e6 h2h1Q+ Kg2xh1 Nf7d8 f2f4+ Kg5g4 b7b8Q
11 00:17 1.550.101 93.107 0.00 d7d8N+ Ke6f6 Ra7a6+ Kf6g5 Nd8f7+ Kg5h4 Ra6a4+ d5d4 Ra4xd4+ Ne5g4 Rd4xg4+ f5xg4 b7b8Q h2h1Q+ Kg2xh1 e2e1Q+ Kh1g2 Qe1e4+ Kg2h2 Qe4f4+ Qb8xf4
12 00:18 1.598.607 91.491 0.00 d7d8N+ Ke6f6 Ra7a6+ Kf6g5 Nd8f7+ Kg5h4 Ra6a4+ d5d4 Ra4xd4+ Ne5g4 Rd4xg4+ f5xg4 b7b8Q h2h1Q+ Kg2xh1 e2e1Q+ Kh1g2 Qe1e4+ Kg2h2 Qe4f4+ Qb8xf4
13 00:19 1.705.361 88.838 0.00 d7d8N+ Ke6f6 Ra7a6+ Kf6g5 Nd8f7+ Kg5h4 Ra6a4+ d5d4 Ra4xd4+ Ne5g4 Rd4xg4+ f5xg4 b7b8Q h2h1Q+ Kg2xh1 e2e1Q+ Kh1g2 Qe1e4+ Kg2h2 Qe4f4+ Qb8xf4
14 00:22 1.883.997 85.442 0.00 d7d8N+ Ke6f6 Ra7a6+ Kf6g5 Nd8f7+ Kg5h4 Ra6a4+ d5d4 Ra4xd4+ Ne5g4 Rd4xg4+ f5xg4 b7b8Q h2h1Q+ Kg2xh1 e2e1Q+ Kh1g2 Qe1e4+ Kg2h2 Qe4f4+ Qb8xf4
15 00:28 2.208.255 81.530 0.00 d7d8N+ Ke6f6 Ra7a6+ Kf6g5 Nd8f7+ Kg5h4 Ra6a4+ d5d4 Ra4xd4+ Ne5g4 Rd4xg4+ f5xg4 b7b8Q h2h1Q+ Kg2xh1 e2e1Q+ Kh1g2 Qe1e4+ Kg2h2 Qe4f4+ Qb8xf4
16 00:36 2.772.393 77.710 0.00 d7d8N+ Ke6f6 Ra7a6+ Kf6g5 Nd8f7+ Kg5h4 Ra6a4+ d5d4 Ra4xd4+ Ne5g4 Rd4xg4+ f5xg4 b7b8Q h2h1Q+ Kg2xh1 e2e1Q+ Kh1g2 Qe1e4+ Kg2h2 Qe4f4+ Qb8xf4
17 00:52 3.775.686 74.128 0.00 d7d8N+ Ke6f6 Ra7a6+ Kf6g5 Nd8f7+ Kg5h4 Ra6a4+ d5d4 Ra4xd4+ Ne5g4 Rd4xg4+ f5xg4 b7b8Q h2h1Q+ Kg2xh1 e2e1Q+ Kh1g2 Qe1e4+ Kg2h2 Qe4f4+ Qb8xf4
18 01:19 5.513.989 71.358 0.00 d7d8N+ Ke6f6 Ra7a6+ Kf6g5 Nd8f7+ Kg5h4 Ra6a4+ d5d4 Ra4xd4+ Ne5g4 Rd4xg4+ f5xg4 b7b8Q h2h1Q+ Kg2xh1 e2e1Q+ Kh1g2 Qe1e4+ Kg2h2 Qe4f4+ Qb8xf4
19 02:09 8.692.456 69.075 0.00 d7d8N+ Ke6f6 Ra7a6+ Kf6g5 Nd8f7+ Kg5h4 Ra6a4+ d5d4 Ra4xd4+ Ne5g4 Rd4xg4+ f5xg4 b7b8Q h2h1Q+ Kg2xh1 e2e1Q+ Kh1g2 Qe1e4+ Kg2h2 Qe4f4+ Qb8xf4

FireBird 1.2:

16 00:03 2.979.767 930.000 +4.84 d7d8N+ Ke6f6 Ra7a6+ Kf6g5 Nd8f7+ Kg5h4 Ra6a4+ Ne5g4 Ra4xg4+ h5xg4 b7b8Q h2h1Q+ Kg2xh1 e2e1Q+ Kh1g2 Qe1e4+ Kg2h2 Kh4h5 Qb8d6 g4g3+ Qd6xg3 Qe4e7 Qg3g7 Qe7h4+ Kh2g2 Qh4e4+ f2f3 Qe4e2+ Kg2g3 Qe2e1+ Kg3f4 Qe1d2+ Kf4xf5 Qd2c2+ Kf5e6 Qc2c8+ Ke6xd5 Qc8b7+ Kd5d6 Qb7b6+ Kd6d7 Qb6b7+ Kd7e6 Qb7c8+ Ke6d6 Qc8a6+ Kd6e5 Qa6e2+ Ke5f4 Qe2d2+ Kf4e4 Qd2c2+ Ke4e3 Qc2c1+ Ke3f2 Qc1xa3
17- 00:05 5.166.439 981.000 +4.76 d7d8N+ Ke6f6 Ra7a6+ Kf6g5 Nd8f7+ Kg5h4 Ra6a4+ Ne5g4 Ra4xg4+ h5xg4 b7b8Q h2h1Q+ Kg2xh1 e2e1Q+ Kh1g2 Qe1e4+ Kg2h2 Kh4h5 Qb8d6 g4g3+ Qd6xg3 Qe4e7 Qg3g7 Qe7h4+ Kh2g2 Qh4e4+ f2f3 Qe4e2+ Kg2g3 Qe2e1+ Kg3f4 Qe1d2+ Kf4xf5 Qd2c2+ Kf5e6 Qc2c8+ Ke6xd5 Qc8b7+ Kd5d6 Qb7b6+ Kd6d7 Qb6b7+ Kd7e6 Qb7c8+ Ke6d6 Qc8a6+ Kd6e5 Qa6e2+ Ke5f4 Qe2d2+ Kf4e4 Qd2c2+ Ke4e3 Qc2c1+ Ke3f2 Qc1xa3
17- 00:06 5.936.340 1.002.000 +4.68 d7d8N+ Ke6f6 Ra7a6+ Kf6g5 Nd8f7+ Kg5h4 Ra6a4+ Ne5g4 Ra4xg4+ h5xg4 b7b8Q h2h1Q+ Kg2xh1 e2e1Q+ Kh1g2 Qe1e4+ Kg2h2 Kh4h5 Qb8d6 g4g3+ Qd6xg3 Qe4e7 Qg3g7 Qe7h4+ Kh2g2 Qh4e4+ f2f3 Qe4e2+ Kg2g3 Qe2e1+ Kg3f4 Qe1d2+ Kf4xf5 Qd2c2+ Kf5e6 Qc2c8+ Ke6xd5 Qc8b7+ Kd5d6 Qb7b6+ Kd6d7 Qb6b7+ Kd7e6 Qb7c8+ Ke6d6 Qc8a6+ Kd6e5 Qa6e2+ Ke5f4 Qe2d2+ Kf4e4 Qd2c2+ Ke4e3 Qc2c1+ Ke3f2 Qc1xa3
17- 00:06 6.700.388 1.018.000 +4.56 d7d8N+ Ke6f6 Ra7a6+ Kf6g5 Nd8f7+ Kg5h4 Ra6a4+ Ne5g4 Ra4xg4+ h5xg4 b7b8Q h2h1Q+ Kg2xh1 e2e1Q+ Kh1g2 Qe1e4+ Kg2h2 Kh4h5 Qb8d6 g4g3+ Qd6xg3 Qe4e7 Qg3g7 Qe7h4+ Kh2g2 Qh4e4+ f2f3 Qe4e2+ Kg2g3 Qe2e1+ Kg3f4 Qe1d2+ Kf4xf5 Qd2c2+ Kf5e6 Qc2c8+ Ke6xd5 Qc8b7+ Kd5d6 Qb7b6+ Kd6d7 Qb6b7+ Kd7e6 Qb7c8+ Ke6d6 Qc8a6+ Kd6e5 Qa6e2+ Ke5f4 Qe2d2+ Kf4e4 Qd2c2+ Ke4e3 Qc2c1+ Ke3f2 Qc1xa3
17- 00:07 7.622.920 1.031.000 +4.38 d7d8N+ Ke6f6 b7b8Q h2h1Q+ Kg2xh1 e2e1Q+ Kh1g2 Qe1e4+ Kg2h2 Ne5g4+ Kh2g3
17- 00:08 8.741.053 1.037.000 +4.11 d7d8N+ Ke6f6 b7b8Q h2h1Q+ Kg2xh1 e2e1Q+ Kh1g2 Qe1e4+ Kg2h2 Ne5g4+ Kh2g3
17- 00:09 9.867.741 1.045.000 +3.71 d7d8N+ Ke6f6 b7b8Q h2h1Q+ Kg2xh1 e2e1Q+ Kh1g2 Qe1e4+ Kg2h2 Ne5g4+ Kh2g3
17- 00:11 11.656.868 1.049.000 +3.11 d7d8N+ Ke6f6 b7b8Q h2h1Q+ Kg2xh1 e2e1Q+ Kh1g2 Qe1e4+ Kg2h2 Ne5g4+ Kh2g3
17- 00:14 14.468.757 1.043.000 +2.21 d7d8N+ Ke6f6 b7b8Q h2h1Q+ Kg2xh1 e2e1Q+ Kh1g2 Qe1e4+ Kg2h2 Ne5g4+ Kh2g3
17- 00:18 19.178.350 1.041.000 +0.86 d7d8N+ Ke6f6 b7b8Q h2h1Q+ Kg2xh1 e2e1Q+ Kh1g2 Qe1e4+ Kg2h2 Ne5g4+ Kh2g3
17 00:21 22.209.474 1.050.000 0.00 d7d8N+ Ke6f6 b7b8Q h2h1Q+ Kg2xh1 e2e1Q+ Kh1g2 Qe1e4+ Kg2f1 Qe4c4+ Kf1g2 Qc4e4+
17 00:25 25.745.707 1.037.000 0.00 d7d8N+ Ke6f6 b7b8Q h2h1Q+ Kg2xh1 e2e1Q+ Kh1g2 Qe1e4+ Kg2f1 Qe4c4+ Kf1g2 Qc4e4+
18 00:27 28.367.936 1.044.000 0.00 d7d8N+ Ke6f6 b7b8Q h2h1Q+ Kg2xh1 e2e1Q+ Kh1g2 Qe1e4+ Kg2f1 Qe4c4+ Kf1g2 Qc4e4+
18 00:34 35.429.801 1.028.000 0.00 d7d8N+ Ke6f6 b7b8Q h2h1Q+ Kg2xh1 e2e1Q+ Kh1g2 Qe1e4+ Kg2f1 Qe4c4+ Kf1g2 Qc4e4+
19+ 00:35 36.392.393 1.031.000 +0.08 d7d8N+ Ke6f6 b7b8Q h2h1Q+ Kg2xh1 e2e1Q+ Kh1g2 Qe1e4+ Kg2f1 Qe4c4+ Kf1g2 Qc4e4+
19+ 00:35 36.392.393 1.031.000 +0.08 d7d8N+ Ke6f6 b7b8Q h2h1Q+ Kg2xh1 e2e1Q+ Kh1g2 Qe1e4+ Kg2f1 Qe4c4+ Kf1g2 Qc4e4+
19+ 00:35 36.515.911 1.030.000 +0.16 d7d8N+ Ke6f6 Ra7a6+ Kf6g5 Nd8f7+ Kg5h4 Ra6a4+ d5d4 Ra4xd4+ Ne5g4 Rd4xg4+ f5xg4 b7b8B h2h1Q+ Kg2xh1 Kh4h3 Nf7g5+ Kh3h4 Ng5f7
19+ 00:35 36.515.911 1.030.000 +0.16 d7d8N+ Ke6f6 Ra7a6+ Kf6g5 Nd8f7+ Kg5h4 Ra6a4+ d5d4 Ra4xd4+ Ne5g4 Rd4xg4+ f5xg4 b7b8B h2h1Q+ Kg2xh1 Kh4h3 Nf7g5+ Kh3h4 Ng5f7
19+ 00:35 36.663.125 1.030.000 +0.28 d7d8N+ Ke6f6 Ra7a6+ Kf6g5 Nd8f7+ Kg5h4 Ra6a4+ d5d4 Ra4xd4+ Ne5g4 Rd4xg4+ f5xg4 b7b8B h2h1Q+ Kg2xh1 Kh4h3 Nf7g5+ Kh3h4 Ng5f7
19+ 00:35 36.663.125 1.030.000 +0.28 d7d8N+ Ke6f6 Ra7a6+ Kf6g5 Nd8f7+ Kg5h4 Ra6a4+ d5d4 Ra4xd4+ Ne5g4 Rd4xg4+ f5xg4 b7b8B h2h1Q+ Kg2xh1 Kh4h3 Nf7g5+ Kh3h4 Ng5f7
19+ 00:36 37.169.452 1.029.000 +0.46 d7d8N+ Ke6f6 Ra7a6+ Kf6g5 Nd8f7+ Kg5h4 Ra6a4+ d5d4 Ra4xd4+ Ne5g4 Rd4xg4+ f5xg4 b7b8B h2h1Q+ Kg2xh1 Kh4h3 Nf7g5+ Kh3h4 Ng5f7
19+ 00:36 37.169.452 1.029.000 +0.46 d7d8N+ Ke6f6 Ra7a6+ Kf6g5 Nd8f7+ Kg5h4 Ra6a4+ d5d4 Ra4xd4+ Ne5g4 Rd4xg4+ f5xg4 b7b8B h2h1Q+ Kg2xh1 Kh4h3 Nf7g5+ Kh3h4 Ng5f7
19+ 00:36 37.602.885 1.028.000 +0.73 d7d8N+ Ke6f6 Ra7a6+ Kf6g5 Nd8f7+ Kg5h4 Ra6a4+ d5d4 Ra4xd4+ Ne5g4 Rd4xg4+ f5xg4 b7b8B h2h1Q+ Kg2xh1 Kh4h3 Nf7g5+ Kh3h4 Ng5f7
19+ 00:36 37.602.885 1.028.000 +0.73 d7d8N+ Ke6f6 Ra7a6+ Kf6g5 Nd8f7+ Kg5h4 Ra6a4+ d5d4 Ra4xd4+ Ne5g4 Rd4xg4+ f5xg4 b7b8B h2h1Q+ Kg2xh1 Kh4h3 Nf7g5+ Kh3h4 Ng5f7
19+ 00:37 38.073.435 1.029.000 +1.13 d7d8N+ Ke6f6 Ra7a6+ Kf6g5 Nd8f7+ Kg5h4 Ra6a4+ d5d4 Ra4xd4+ Ne5g4 Rd4xg4+ f5xg4 b7b8B h2h1Q+ Kg2xh1 Kh4h3 Nf7g5+ Kh3h4 Bb8g3+ Kh4xg5 f2f4+ g4xf3/ep a3a4 Kg5f5 a4a5 Kf5e4 Kh1g1 Ke4d4 Kg1f2
19+ 00:37 38.073.435 1.029.000 +1.13 d7d8N+ Ke6f6 Ra7a6+ Kf6g5 Nd8f7+ Kg5h4 Ra6a4+ d5d4 Ra4xd4+ Ne5g4 Rd4xg4+ f5xg4 b7b8B h2h1Q+ Kg2xh1 Kh4h3 Nf7g5+ Kh3h4 Bb8g3+ Kh4xg5 f2f4+ g4xf3/ep a3a4 Kg5f5 a4a5 Kf5e4 Kh1g1 Ke4d4 Kg1f2
19+ 00:38 40.010.234 1.037.000 +1.73 d7d8N+ Ke6f6 Ra7a6+ Kf6g5 Nd8f7+ Kg5h4 Ra6a4+ d5d4 Ra4xd4+ Ne5g4 Rd4xg4+ f5xg4 b7b8B h2h1Q+ Kg2xh1 Kh4h3 Nf7g5+ Kh3h4 Bb8g3+ Kh4xg5 f2f4+ g4xf3/ep a3a4 Kg5g6 Kh1g1 h5h4 Bg3xh4 Kg6f5 Kg1f2 Kf5g4 Bh4g3 e2e1Q+ Kf2xe1 Kg4xg3 Ke1f1 Kg3f4 Kf1f2
19+ 00:38 40.010.234 1.037.000 +1.73 d7d8N+ Ke6f6 Ra7a6+ Kf6g5 Nd8f7+ Kg5h4 Ra6a4+ d5d4 Ra4xd4+ Ne5g4 Rd4xg4+ f5xg4 b7b8B h2h1Q+ Kg2xh1 Kh4h3 Nf7g5+ Kh3h4 Bb8g3+ Kh4xg5 f2f4+ g4xf3/ep a3a4 Kg5g6 Kh1g1 h5h4 Bg3xh4 Kg6f5 Kg1f2 Kf5g4 Bh4g3 e2e1Q+ Kf2xe1 Kg4xg3 Ke1f1 Kg3f4 Kf1f2
19+ 00:40 41.575.630 1.044.000 +2.63 d7d8N+ Ke6f6 Ra7a6+ Kf6g5 Nd8f7+ Kg5h4 Ra6a4+ d5d4 Ra4xd4+ Ne5g4 Rd4xg4+ f5xg4 b7b8B h2h1Q+ Kg2xh1 Kh4h3 Nf7g5+ Kh3h4 Ng5f7
19+ 00:40 41.575.630 1.044.000 +2.63 d7d8N+ Ke6f6 Ra7a6+ Kf6g5 Nd8f7+ Kg5h4 Ra6a4+ d5d4 Ra4xd4+ Ne5g4 Rd4xg4+ f5xg4 b7b8B h2h1Q+ Kg2xh1 Kh4h3 Nf7g5+ Kh3h4 Ng5f7
19+ 00:43 46.313.345 1.075.000 +3.98 d7d8N+ Ke6f6 Ra7a6+ Kf6g5 Nd8f7+ Kg5h4 Ra6a4+ d5d4 Ra4xd4+ Ne5g4 Rd4xg4+ f5xg4 b7b8B h2h1Q+ Kg2xh1 Kh4h3 Nf7g5+ Kh3h4 Bb8g3+ Kh4xg5 f2f4+ g4xf3/ep a3a4 Kg5f5 a4a5 h5h4 Bg3f2 e2e1R+ Bf2xe1 Kf5e4 Be1xh4 Ke4d5 Kh1g1
19+ 00:43 46.313.345 1.075.000 +3.98 d7d8N+ Ke6f6 Ra7a6+ Kf6g5 Nd8f7+ Kg5h4 Ra6a4+ d5d4 Ra4xd4+ Ne5g4 Rd4xg4+ f5xg4 b7b8B h2h1Q+ Kg2xh1 Kh4h3 Nf7g5+ Kh3h4 Bb8g3+ Kh4xg5 f2f4+ g4xf3/ep a3a4 Kg5f5 a4a5 h5h4 Bg3f2 e2e1R+ Bf2xe1 Kf5e4 Be1xh4 Ke4d5 Kh1g1
19 00:46 50.296.347 1.093.000 +4.73 d7d8N+ Ke6f6 Ra7a6+ Kf6g5 Nd8f7+ Kg5h4 Ra6a4+ d5d4 Ra4xd4+ Ne5g4 Rd4xg4+ f5xg4 b7b8B h2h1Q+ Kg2xh1 e2e1Q+ Kh1g2 Qe1e4+ Kg2h2 g4g3+ Bb8xg3+ Kh4g4 f2f3+ Kg4xf3 Nf7g5+ Kf3e3 Bg3f2+ Ke3xf2 Ng5xe4+ Kf2e3 Ne4c3 Ke3d4 a3a4 Kd4c5 Kh2h3 Kc5b4 Kh3h4 Kb4a5 Kh4xh5 Ka5a6 Kh5g5 Ka6b6 Kg5f5 Kb6a5 Kf5e5
19 00:47 51.656.339 1.088.000 +4.73 d7d8N+ Ke6f6 Ra7a6+ Kf6g5 Nd8f7+ Kg5h4 Ra6a4+ d5d4 Ra4xd4+ Ne5g4 Rd4xg4+ f5xg4 b7b8B h2h1Q+ Kg2xh1 e2e1Q+ Kh1g2 Qe1e4+ Kg2h2 g4g3+ Bb8xg3+ Kh4g4 f2f3+ Kg4xf3 Nf7g5+ Kf3e3 Bg3f2+ Ke3xf2 Ng5xe4+ Kf2e3 Ne4c3 Ke3d4 a3a4 Kd4c5 Kh2h3 Kc5b4 Kh3h4 Kb4a5 Kh4xh5 Ka5a6 Kh5g5 Ka6b6 Kg5f5 Kb6a5 Kf5e5
20+ 00:50 56.065.259 1.115.000 +4.81 d7d8N+ Ke6f6 Ra7a6+ Kf6g5 Nd8f7+ Kg5h4 Ra6a4+ d5d4 Ra4xd4+ Ne5g4 Rd4xg4+ f5xg4 b7b8B h2h1Q+ Kg2xh1 e2e1Q+ Kh1g2 Qe1e4+ Kg2h2 g4g3+ Bb8xg3+ Kh4g4 f2f3+ Kg4xf3 Nf7g5+ Kf3e3 Bg3f2+ Ke3xf2 Ng5xe4+ Kf2e3 Ne4c3 Ke3d4 a3a4 Kd4c5 Kh2h3 Kc5b4 Kh3h4 Kb4a5 Kh4xh5 Ka5a6 Kh5g5 Ka6b6 Kg5f5 Kb6a5 Kf5e5 Ka5b4
20+ 00:50 56.065.259 1.115.000 +4.81 d7d8N+ Ke6f6 Ra7a6+ Kf6g5 Nd8f7+ Kg5h4 Ra6a4+ d5d4 Ra4xd4+ Ne5g4 Rd4xg4+ f5xg4 b7b8B h2h1Q+ Kg2xh1 e2e1Q+ Kh1g2 Qe1e4+ Kg2h2 g4g3+ Bb8xg3+ Kh4g4 f2f3+ Kg4xf3 Nf7g5+ Kf3e3 Bg3f2+ Ke3xf2 Ng5xe4+ Kf2e3 Ne4c3 Ke3d4 a3a4 Kd4c5 Kh2h3 Kc5b4 Kh3h4 Kb4a5 Kh4xh5 Ka5a6 Kh5g5 Ka6b6 Kg5f5 Kb6a5 Kf5e5 Ka5b4
20 00:52 58.594.266 1.117.000 +4.80 d7d8N+ Ke6f6 Ra7a6+ Kf6g5 Nd8f7+ Kg5h4 Ra6a4+ d5d4 Ra4xd4+ Ne5g4 Rd4xg4+ f5xg4 b7b8B h2h1Q+ Kg2xh1 e2e1Q+ Kh1g2 Qe1e4+ Kg2h2 g4g3+ Bb8xg3+ Kh4g4 f2f3+ Kg4xf3 Nf7g5+ Kf3e3 Bg3f2+ Ke3xf2 Ng5xe4+ Kf2e3 Ne4c3 Ke3d4 a3a4 Kd4c5 Kh2h3 Kc5b4 Kh3h4 Kb4a5 Kh4xh5 Ka5a6 Kh5g4 Ka6b6 Kg4f5 Kb6a6 Kf5e5 Ka6a5 Ke5d4 Ka5b4 a2a3+ Kb4a5
20 00:55 61.895.939 1.110.000 +4.80 d7d8N+ Ke6f6 Ra7a6+ Kf6g5 Nd8f7+ Kg5h4 Ra6a4+ d5d4 Ra4xd4+ Ne5g4 Rd4xg4+ f5xg4 b7b8B h2h1Q+ Kg2xh1 e2e1Q+ Kh1g2 Qe1e4+ Kg2h2 g4g3+ Bb8xg3+ Kh4g4 f2f3+ Kg4xf3 Nf7g5+ Kf3e3 Bg3f2+ Ke3xf2 Ng5xe4+ Kf2e3 Ne4c3 Ke3d4 a3a4 Kd4c5 Kh2h3 Kc5b4 Kh3h4 Kb4a5 Kh4xh5 Ka5a6 Kh5g4 Ka6b6 Kg4f5 Kb6a6 Kf5e5 Ka6a5 Ke5d4 Ka5b4 a2a3+ Kb4a5
21 01:03 70.155.295 1.116.000 +4.83 d7d8N+ Ke6f6 Ra7a6+ Kf6g5 Nd8f7+ Kg5h4 Ra6a4+ d5d4 Ra4xd4+ Ne5g4 Rd4xg4+ f5xg4 b7b8B h2h1Q+ Kg2xh1 e2e1Q+ Kh1g2 Qe1e4+ Kg2h2 g4g3+ Bb8xg3+ Kh4g4 f2f3+ Kg4xf3 Nf7g5+ Kf3e3 Bg3f2+ Ke3xf2 Ng5xe4+ Kf2e3 Ne4c3 Ke3d4 a3a4 Kd4c5 Kh2h3 Kc5b4 Kh3h4 Kb4a5 Kh4xh5 Ka5a6 Kh5g5 Ka6b6 Kg5f5 Kb6a6 Kf5e6 Ka6a5 Ke6d7 Ka5b4 Kd7c6
21 01:10 77.381.416 1.107.000 +4.83 d7d8N+ Ke6f6 Ra7a6+ Kf6g5 Nd8f7+ Kg5h4 Ra6a4+ d5d4 Ra4xd4+ Ne5g4 Rd4xg4+ f5xg4 b7b8B h2h1Q+ Kg2xh1 e2e1Q+ Kh1g2 Qe1e4+ Kg2h2 g4g3+ Bb8xg3+ Kh4g4 f2f3+ Kg4xf3 Nf7g5+ Kf3e3 Bg3f2+ Ke3xf2 Ng5xe4+ Kf2e3 Ne4c3 Ke3d4 a3a4 Kd4c5 Kh2h3 Kc5b4 Kh3h4 Kb4a5 Kh4xh5 Ka5a6 Kh5g5 Ka6b6 Kg5f5 Kb6a6 Kf5e6 Ka6a5 Ke6d7 Ka5b4 Kd7c6
22 01:24 93.488.368 1.112.000 +4.83 d7d8N+ Ke6f6 Ra7a6+ Kf6g5 Nd8f7+ Kg5h4 Ra6a4+ d5d4 Ra4xd4+ Ne5g4 Rd4xg4+ f5xg4 b7b8B h2h1Q+ Kg2xh1 e2e1Q+ Kh1g2 Qe1e4+ Kg2h2 g4g3+ Bb8xg3+ Kh4g4 f2f3+ Kg4xf3 Nf7g5+ Kf3e3 Bg3f2+ Ke3xf2 Ng5xe4+ Kf2e3 Ne4c3 Ke3d4 a3a4 Kd4c5 Kh2h3 Kc5b4 Kh3h4 Kb4a5 Kh4xh5 Ka5a6 Kh5g5 Ka6b6 Kg5f6 Kb6a6 Kf6e6 Ka6a5 Ke6d7 Ka5b4 Kd7c6
22 01:39 109.042.730 1.102.000 +4.83 d7d8N+ Ke6f6 Ra7a6+ Kf6g5 Nd8f7+ Kg5h4 Ra6a4+ d5d4 Ra4xd4+ Ne5g4 Rd4xg4+ f5xg4 b7b8B h2h1Q+ Kg2xh1 e2e1Q+ Kh1g2 Qe1e4+ Kg2h2 g4g3+ Bb8xg3+ Kh4g4 f2f3+ Kg4xf3 Nf7g5+ Kf3e3 Bg3f2+ Ke3xf2 Ng5xe4+ Kf2e3 Ne4c3 Ke3d4 a3a4 Kd4c5 Kh2h3 Kc5b4 Kh3h4 Kb4a5 Kh4xh5 Ka5a6 Kh5g5 Ka6b6 Kg5f6 Kb6a6 Kf6e6 Ka6a5 Ke6d7 Ka5b4 Kd7c6
23+ 01:56 128.213.191 1.106.000 +4.91 d7d8N+ Ke6f6 Ra7a6+ Kf6g5 Nd8f7+ Kg5h4 Ra6a4+ d5d4 Ra4xd4+ Ne5g4 Rd4xg4+ f5xg4 b7b8B h2h1Q+ Kg2xh1 e2e1Q+ Kh1g2 Qe1e4+ Kg2h2 g4g3+ Bb8xg3+ Kh4g4 f2f3+ Kg4xf3 Nf7g5+ Kf3e3 Bg3f2+ Ke3xf2 Ng5xe4+ Kf2e3 Ne4c3 Ke3d4 a3a4 Kd4c5 Kh2h3 Kc5b4 Kh3h4 Kb4a5 Kh4xh5 Ka5a6 Kh5g5 Ka6b6 Kg5f5 Kb6a5 Kf5g6 Ka5a6 Kg6h5 Ka6a5 Kh5g5 Ka5a6 Kg5g4 Ka6b6 Kg4g5 Kb6a6
23+ 01:56 128.213.191 1.106.000 +4.91 d7d8N+ Ke6f6 Ra7a6+ Kf6g5 Nd8f7+ Kg5h4 Ra6a4+ d5d4 Ra4xd4+ Ne5g4 Rd4xg4+ f5xg4 b7b8B h2h1Q+ Kg2xh1 e2e1Q+ Kh1g2 Qe1e4+ Kg2h2 g4g3+ Bb8xg3+ Kh4g4 f2f3+ Kg4xf3 Nf7g5+ Kf3e3 Bg3f2+ Ke3xf2 Ng5xe4+ Kf2e3 Ne4c3 Ke3d4 a3a4 Kd4c5 Kh2h3 Kc5b4 Kh3h4 Kb4a5 Kh4xh5 Ka5a6 Kh5g5 Ka6b6 Kg5f5 Kb6a5 Kf5g6 Ka5a6 Kg6h5 Ka6a5 Kh5g5 Ka5a6 Kg5g4 Ka6b6 Kg4g5 Kb6a6
23 02:14 150.577.357 1.118.000 +4.91 d7d8N+ Ke6f6 Ra7a6+ Kf6g5 Nd8f7+ Kg5h4 Ra6a4+ d5d4 Ra4xd4+ Ne5g4 Rd4xg4+ f5xg4 b7b8B h2h1Q+ Kg2xh1 e2e1Q+ Kh1g2 Qe1e4+ Kg2h2 g4g3+ Bb8xg3+ Kh4g4 f2f3+ Kg4xf3 Nf7g5+ Kf3e3 Bg3f2+ Ke3xf2 Ng5xe4+ Kf2e3 Ne4c3 Ke3d4 a3a4 Kd4c5 Kh2h3 Kc5b4 Kh3h4 Kb4a5 Kh4xh5 Ka5a6 Kh5g5 Ka6b6 Kg5f6 Kb6a6 Kf6e6 Ka6a5 Ke6d7 Ka5b6 Nc3d5+ Kb6a5
23 02:52 192.429.785 1.114.000 +4.91 d7d8N+ Ke6f6 Ra7a6+ Kf6g5 Nd8f7+ Kg5h4 Ra6a4+ d5d4 Ra4xd4+ Ne5g4 Rd4xg4+ f5xg4 b7b8B h2h1Q+ Kg2xh1 e2e1Q+ Kh1g2 Qe1e4+ Kg2h2 g4g3+ Bb8xg3+ Kh4g4 f2f3+ Kg4xf3 Nf7g5+ Kf3e3 Bg3f2+ Ke3xf2 Ng5xe4+ Kf2e3 Ne4c3 Ke3d4 a3a4 Kd4c5 Kh2h3 Kc5b4 Kh3h4 Kb4a5 Kh4xh5 Ka5a6 Kh5g5 Ka6b6 Kg5f6 Kb6a6 Kf6e6 Ka6a5 Ke6d7 Ka5b6 Nc3d5+ Kb6a5
24+ 03:15 218.907.515 1.122.000 +4.99 d7d8N+ Ke6f6 Ra7a6+ Kf6g5 Nd8f7+ Kg5h4 Ra6a4+ d5d4 Ra4xd4+ Ne5g4 Rd4xg4+ f5xg4 b7b8B h2h1Q+ Kg2xh1 e2e1Q+ Kh1g2 Qe1e4+ Kg2h2 g4g3+ Bb8xg3+ Kh4g4 f2f3+ Kg4xf3 Nf7g5+ Kf3e3 Bg3f2+ Ke3xf2 Ng5xe4+ Kf2e3 Ne4c3 Ke3d4 a3a4 Kd4c5 Kh2h3 Kc5b4 Kh3h4 Kb4a5 Kh4xh5 Ka5a6 Kh5g5 Ka6b6 Kg5f6 Kb6a6 Kf6g6 Ka6b6 Kg6f5 Kb6a6 Kf5e5 Ka6a5 Ke5d4 Ka5b4 a2a3+ Kb4a5
24+ 03:15 218.907.515 1.122.000 +4.99 d7d8N+ Ke6f6 Ra7a6+ Kf6g5 Nd8f7+ Kg5h4 Ra6a4+ d5d4 Ra4xd4+ Ne5g4 Rd4xg4+ f5xg4 b7b8B h2h1Q+ Kg2xh1 e2e1Q+ Kh1g2 Qe1e4+ Kg2h2 g4g3+ Bb8xg3+ Kh4g4 f2f3+ Kg4xf3 Nf7g5+ Kf3e3 Bg3f2+ Ke3xf2 Ng5xe4+ Kf2e3 Ne4c3 Ke3d4 a3a4 Kd4c5 Kh2h3 Kc5b4 Kh3h4 Kb4a5 Kh4xh5 Ka5a6 Kh5g5 Ka6b6 Kg5f6 Kb6a6 Kf6g6 Ka6b6 Kg6f5 Kb6a6 Kf5e5 Ka6a5 Ke5d4 Ka5b4 a2a3+ Kb4a5
24+ 03:35 245.764.688 1.143.000 +5.07 d7d8N+ Ke6f6 Ra7a6+ Kf6g5 Nd8f7+ Kg5h4 Ra6a4+ d5d4 Ra4xd4+ Ne5g4 Rd4xg4+ f5xg4 b7b8B h2h1Q+ Kg2xh1 e2e1Q+ Kh1g2 Qe1e4+ Kg2h2 g4g3+ Bb8xg3+ Kh4g4 f2f3+ Kg4xf3 Nf7g5+ Kf3e3 Bg3f2+ Ke3xf2 Ng5xe4+ Kf2e3 Ne4c3 Ke3d4 a3a4 Kd4c5 Kh2h3 Kc5b4 Kh3h4 Kb4a5 Kh4xh5 Ka5a6 Kh5g5 Ka6b6 Kg5f6 Kb6a6 Kf6g6 Ka6b6 Kg6f5 Kb6a6 Kf5g5
24+ 03:35 245.764.688 1.143.000 +5.07 d7d8N+ Ke6f6 Ra7a6+ Kf6g5 Nd8f7+ Kg5h4 Ra6a4+ d5d4 Ra4xd4+ Ne5g4 Rd4xg4+ f5xg4 b7b8B h2h1Q+ Kg2xh1 e2e1Q+ Kh1g2 Qe1e4+ Kg2h2 g4g3+ Bb8xg3+ Kh4g4 f2f3+ Kg4xf3 Nf7g5+ Kf3e3 Bg3f2+ Ke3xf2 Ng5xe4+ Kf2e3 Ne4c3 Ke3d4 a3a4 Kd4c5 Kh2h3 Kc5b4 Kh3h4 Kb4a5 Kh4xh5 Ka5a6 Kh5g5 Ka6b6 Kg5f6 Kb6a6 Kf6g6 Ka6b6 Kg6f5 Kb6a6 Kf5g5
24+ 04:01 282.635.860 1.172.000 +5.19 d7d8N+ Ke6f6 Ra7a6+ Kf6g5 Nd8f7+ Kg5h4 Ra6a4+ d5d4 Ra4xd4+ Ne5g4 Rd4xg4+ f5xg4 b7b8B h2h1Q+ Kg2xh1 e2e1Q+ Kh1g2 Qe1e4+ Kg2h2 g4g3+ Bb8xg3+ Kh4g4 f2f3+ Kg4xf3 Nf7g5+ Kf3e3 Bg3f2+ Ke3xf2 Ng5xe4+ Kf2e3 Ne4c3 Ke3d4 a3a4 Kd4c5 Kh2h3 Kc5b4 Kh3h4 Kb4a5 Kh4xh5 Ka5a6 Kh5g5 Ka6b6 Kg5f5 Kb6a6 Kf5g5
24+ 04:01 282.635.860 1.172.000 +5.19 d7d8N+ Ke6f6 Ra7a6+ Kf6g5 Nd8f7+ Kg5h4 Ra6a4+ d5d4 Ra4xd4+ Ne5g4 Rd4xg4+ f5xg4 b7b8B h2h1Q+ Kg2xh1 e2e1Q+ Kh1g2 Qe1e4+ Kg2h2 g4g3+ Bb8xg3+ Kh4g4 f2f3+ Kg4xf3 Nf7g5+ Kf3e3 Bg3f2+ Ke3xf2 Ng5xe4+ Kf2e3 Ne4c3 Ke3d4 a3a4 Kd4c5 Kh2h3 Kc5b4 Kh3h4 Kb4a5 Kh4xh5 Ka5a6 Kh5g5 Ka6b6 Kg5f5 Kb6a6 Kf5g5
24+ 05:01 391.345.027 1.297.000 +5.37 d7d8N+ Ke6f6 Ra7a6+ Kf6g5 Nd8f7+ Kg5h4 Ra6a4+ d5d4 Ra4xd4+ Ne5g4 Rd4xg4+ f5xg4 b7b8B h2h1Q+ Kg2xh1 e2e1Q+ Kh1g2 Qe1e4+ Kg2h2 g4g3+ Bb8xg3+ Kh4g4 f2f3+ Kg4xf3 Nf7g5+ Kf3e3 Bg3f2+ Ke3xf2 Ng5xe4+ Kf2e3 Ne4c5 Ke3d4 Nc5b3+ Kd4d5 a3a4 Kd5e6 a4a5 Ke6d5 Kh2h3 Kd5d6 Kh3h4 Kd6c7 Nb3c5 Kc7b8 Kh4xh5 Kb8a7 Kh5g5 Ka7b8 Kg5f5 Kb8a7 Kf5e5
24+ 05:01 391.345.027 1.297.000 +5.37 d7d8N+ Ke6f6 Ra7a6+ Kf6g5 Nd8f7+ Kg5h4 Ra6a4+ d5d4 Ra4xd4+ Ne5g4 Rd4xg4+ f5xg4 b7b8B h2h1Q+ Kg2xh1 e2e1Q+ Kh1g2 Qe1e4+ Kg2h2 g4g3+ Bb8xg3+ Kh4g4 f2f3+ Kg4xf3 Nf7g5+ Kf3e3 Bg3f2+ Ke3xf2 Ng5xe4+ Kf2e3 Ne4c5 Ke3d4 Nc5b3+ Kd4d5 a3a4 Kd5e6 a4a5 Ke6d5 Kh2h3 Kd5d6 Kh3h4 Kd6c7 Nb3c5 Kc7b8 Kh4xh5 Kb8a7 Kh5g5 Ka7b8 Kg5f5 Kb8a7 Kf5e5

[lmader]

The entire line is forced.

Here's the problem with Rybka's evaluation:

19 02:09 8.692.456 69.075 0.00 d7d8N+ Ke6f6 Ra7a6+ Kf6g5 Nd8f7+ Kg5h4 Ra6a4+ d5d4 Ra4xd4+ Ne5g4 Rd4xg4+ f5xg4 b7b8Q

The last move shown above in Rybka's PV, b7b8Q, needs to be an underpromotion to a bishop for white to win. Rybka's line leads to a stalemate. Both Stockfish and Firebird see it correctly.

[Dann Corbit]

The entire line is forced.

Here's the problem with Rybka's evaluation:

19 02:09 8.692.456 69.075 0.00 d7d8N+ Ke6f6 Ra7a6+ Kf6g5 Nd8f7+ Kg5h4 Ra6a4+ d5d4 Ra4xd4+ Ne5g4 Rd4xg4+ f5xg4 b7b8Q

The last move shown above in Rybka's PV, b7b8Q, needs to be an underpromotion to a bishop for white to win. Rybka's line leads to a stalemate. Both Stockfish and Firebird see it correctly.

Well known that Rybka actually cannot underpromote to bishop.
Only queen and knight, if I recall correctly.

[Sven]

The entire line is forced.

Here's the problem with Rybka's evaluation:

19 02:09 8.692.456 69.075 0.00 d7d8N+ Ke6f6 Ra7a6+ Kf6g5 Nd8f7+ Kg5h4 Ra6a4+ d5d4 Ra4xd4+ Ne5g4 Rd4xg4+ f5xg4 b7b8Q

The last move shown above in Rybka's PV, b7b8Q, needs to be an underpromotion to a bishop for white to win. Rybka's line leads to a stalemate. Both Stockfish and Firebird see it correctly.

Well known that Rybka actually cannot underpromote to bishop.
Only queen and knight, if I recall correctly.

Queen + knight + rook. Only bishop excluded, a change would require redesign of the move data structure according to some post of Vas long ago in the Rybka forum. And the restriction does only affect search but a legal user move that promotes to bishop is accepted of course.

Sven

[David Dahlem]

Two more engines with the same problem:

Komodo 1.0:

21 00:43 20.245.868 469.469 0.00 d7d8Q h2h1Q+ Kg2xh1 e2e1Q+ Kh1g2 Qe1e4+ Kg2f1 Qe4b1+ Kf1g2 Qb1e4+

Spark 0.3a:

11/26 00:02 1.795.784 732.076 +4.53 d7d8N+ Ke6f6 Ra7a6+ Kf6g5 Nd8f7+ Ne5xf7 Ra6e6 Nf7d8 b7b8Q Nd8xe6 Qb8e5 Ne6f4+ Kg2xh2 d5d4 Kh2g3
17/44 01:48 92.164.231 854.115 +0.04 d7d8N+ Ke6f6 Ra7a6+ Kf6g5 Nd8f7+ Kg5h4 Ra6a4+ d5d4 Ra4xd4+ Ne5g4 Rd4xg4+ f5xg4 b7b8B h2h1Q+ Kg2xh1 e2e1Q+ Kh1g2 Qe1e4+ Kg2h2 g4g3+ Bb8xg3+ Kh4g4 f2f3+ Kg4xf3 Nf7g5+ Kf3e3 Bg3f2+ Ke3d3 Ng5xe4 Kd3xe4 Kh2h3 h5h4 Bf2xh4 Ke4d3

[lmader]

I don't think that these engines are exhibiting the bishop under-promotion bug. I think you just need to give them more time to calculate. It can take a lot of time on this position.