Consider the following position: 2r5/1K6/P1B5/8/4p1pp/8/3R1PkP/8 w - - 0 1. After the move f4, putting Black under a discovered check, StockNemo 5.7.0.0 says the best move is exf3. This is, however, illegal since Black is under check even after the move, and White captures Black's king in the following move.
Consider the following position:
2r5/1K6/P1B5/8/4p1pp/8/3R1PkP/8 w - - 0 1. After the movef4, putting Black under a discovered check, StockNemo 5.7.0.0 says the best move isexf3. This is, however, illegal since Black is under check even after the move, and White captures Black's king in the following move.