Pawns occasionally taking sideways

The chess computer occasionally has pawns takes another pawn that is ajacent (ie sideways and not diagonally) and the pawn ends up diagonally in front of the piece it's just taken. Today a human opponent did the same. Is this a known bug in the software or a rule I never knew about? 

This is 'en passant' capturing. The last rule that folks usually learn about. 

This may be the first time you experience this, but is probably my tenth time (or even more) I read the same issue again.

https://www.chess.com/article/view/his-pawn-cheated-and-killed-my-pawn

You are not the only one.

I learnt the en passant not long after I experienced this "glitch". This was more than ten years ago.

i instruct my pawns to take every which way.

Won't ever happen if I play without pawns.

Peonies, on the other hand...

Press coverage on new Catholic rule:

It's a glitch. You should definitely report that

En passant.