Wrong pawn movement

I don't know if this is a bug, but this happened to me already twice, en.lichess.org/KBnQrG481qEs just check 11-12 moves and how the trade is done

12. dxe6 is a legal move called en passent.

Haha!

"En passant (from French: in passing) is a move in chess.[1] It is a special pawn capture, that can only occur immediately after a pawn moves two ranks forward from its starting position and an enemy pawn could have captured it had the pawn moved only one square forward (the capturing pawn must be on its fifth rank prior to executing this maneuver). The opponent captures the just-moved pawn "as it passes" through the first square. The resulting position is the same as if the pawn had moved only one square forward and the enemy pawn had captured it normally."

Source: en.m.wikipedia.org/wiki/En_passant

Just reading the title I know the answer already. The twin topic is "castling bug"...

Guys, it ain't a bug it's a feature. I recommend you to learn the chess rules before you play.

For the curious about where to learn the rules:
en.lichess.org/learn

As for threefold repetition rules, please reference FIDE Laws of Chess.

The Q&A section could maybe have a section divided into categorys where frequently asked questions are listed. Many beginners might be unfamiliar with castling and ep.

Also many players banned for cheat wonder why they can't play.

Another very frequently asked question is players that get the message "Cheat detected" during a game and don't understand they cheated.