I know this isn't a Transformice bug, if there's a better place to post this please tell me, but the game is playable via Transformice and isn't a module.

The bug occurs when you have an en passant move as a pawn. If however, before the timer runs out and a team-mate's piece (though I've only witnessed this bug myself with a team-mate's pawn) also takes, and moves into the space where the en passant take would be, you can take your own team-mate's piece. Note, this only works if two different players are controlling the pieces (otherwise when you go to take your own team mate's piece the game defaults to selecting the piece instead of taking).

I hope that makes sense, it's tricky to explain, but if anyone wants a demo of the bug contact me on Transformice.

Here are two screenshots as best as I can show the bug occurring: [url=https://imgur.com/M3Bapx6,I28EfHF](Imgur album)[/url] The second screenshot in particular shows in the captured pieces list that I have captured my own team-mate's piece.