Bug in a game

I was playing a game and when my opponent moved a pawn directly forward, it also killed my pawn.

http://es.lichess.org/sYoBDvhs

Move 27. I want my points reinstated.

Its not the bug. Its en passant rule :) You can read more here
en.wikipedia.org/wiki/En_passant

What #2 said.

When an enemy pawn is on your fourth rank, it should, by rights, restrain adjacent pawns from advancing. However, due to the 'two squares' option on a pawn's first move, it can effectively bypass the restraining enemy pawn. In order to restore the defensive value of a far advanced pawn, the 'en passant' rule allows a pawn to be taken *as if it had moved only one square*. So, not a bug :/