I have read that if they pass gass while praying, that is also a major no-no. I don’t know whether their prayers are not accepted, if they have to get up and move to the back row, or even if they are responsible for the guy behind them passing out and hitting his head on the floor.
I have to say that being required to go to the back row seems like a pretty good punishment, although it might just be giving them a view of more temptation.