Zerko
Buggy fullscreen mode
In later levels, say, 39+, if you play in fullscreen mode, you won't see some pieces - they are outside the view area, which covers only the middle square of the screen. Changing to maximized window shows all the play area, including invisible pieces.

This bug is also present in at least one more game you made, though currently I can't remember which one - I have (and played) all of them :)