The weirdest thing to happen to me was way back on ISS deluxe on the SNES...
there was a cheat i discovered on penalties, in that if you were the keeper, if your oponent scored on the standard 'front view' while taking the penalty, you could quickly take control of the keeper when the game switched to the side view and make the keeper dive in a different direction, therefore saving the penalty.
So one time, i did this against my friend, but the keeper dived slightly backwards and went over the goal line with the ball, and the forward stormed in with a sliding tackle and fouled my keeper behind the goal line...so i had a free-kick in my own goal, but it gets weirder.....i took the free-kick, but as soon as the ball crossed the goal line, the screen came up with "goal!", but when we came to kick-off, my friends team had been given 70 goals. the game carried on as normal, but the final score was something like 70-3.