This is definitely not as it is supposed to behave. The chekmate detection does seem to work, though, as can be tested by first playing the (illegal) moves 1.Nb4 Ka7, then switching on the AI and playing 2.Qa6. It then says "I resign" without playing a move. After it lost its King, and it is its turn to move, it should say "It seems I have already lost".
No idea why that wouldn't have worked in the game you played. That it doesn't see mate-in-1 coming is normal; the default lookeahead depth is only 2 ply + quiescence search, and for mated-in-1 the King is only captured on ply 4. (So 3 ply + QS would be enough to see it.)
In any case the play will be quite weak; it is intended to be a demo for people who just have seen the rules for the first time, to get an idea what the game is like. Setting it to 4 ply would make it slightly tougher, but even then a strong player should not have much dificulty beating it. (An for large games like SAC Chess it might think too long.)
This is definitely not as it is supposed to behave. The chekmate detection does seem to work, though, as can be tested by first playing the (illegal) moves 1.Nb4 Ka7, then switching on the AI and playing 2.Qa6. It then says "I resign" without playing a move. After it lost its King, and it is its turn to move, it should say "It seems I have already lost".
No idea why that wouldn't have worked in the game you played. That it doesn't see mate-in-1 coming is normal; the default lookeahead depth is only 2 ply + quiescence search, and for mated-in-1 the King is only captured on ply 4. (So 3 ply + QS would be enough to see it.)
In any case the play will be quite weak; it is intended to be a demo for people who just have seen the rules for the first time, to get an idea what the game is like. Setting it to 4 ply would make it slightly tougher, but even then a strong player should not have much dificulty beating it. (An for large games like SAC Chess it might think too long.)