Why does FRITZ 10 not see Mate in 1

[guyhaw]

I'm checking out SAN-v-LAN with an 'unreal' game and arrive at:
1nkr1bnr/pbpq1ppp/1p1p4/1N6/8/5N2/PPPPBPPP/R1BQ1RK1 w - - 0 9
Here, White has 9.Nxa7# but 'Infinite Analysis' on FRITZ10 grinds on and on without featuring N*a7 in its top 10 moves.
Why is this?
g

[Jouni]

My Fritz says:

Analysis by Fritz 10:

1.Nxa7#
+- (#1) Depth: 5/5 00:00:00 0kN

Jouni