This bug is reproduceable in version 0.3 alpha.
to recreate it, start a game against an AI player.
1) move pawn from f2 to f3. the AI player will move his
pawn from h7 to h5.
2) move pawn from h2 to h3. the AI player will move his
pawn from h5 to h4.
3) move pawn from g2 to g4. the AI player moves to g3,
taking the pawn that is not there.