Well all I know is that the first game I played I could not move the pawn diagonally to capture any piece other than the machines pawn. all my problems happened in player vs machine mode. Now it seems to be working though, so I don't know what happened there.
The game should alert me when my king is in check, and it should alert me/end the game if I am in checkmate, and should not allow me to move my king into check, and should end when my king is taken, that is how chess works. It should especially do these things in player vs machine mode, and player vs player mode but it doesn't...
I don't mean to sound overly critical or negative, and am sorry if I do, I just wish to help you to improve your game.