It's not weird, it's legal move, it is called en passant.
Known glitch? Pawn E5 takes Pawn F5

S'in the roolz dood. http://en.wikipedia.org/wiki/En_passant
It's called "en passant", you are allowed to take the pawn if it advances two squares and ends up beside the opponents pawn, exactly as above.

En passant (from French: in passing) is a move in the board game of chess (Brace 1977). It is a special pawn capture which can occur immediately after a player moves a pawn two squares forward from its starting position, and an opposing pawn could have captured it, had it moved only one square forward. The opponent captures the just-moved pawn as if taking it "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 opposing pawn had captured normally.
http://en.wikipedia.org/wiki/En_passant
Well known...
Weird...