I actually had one very recently, its not so much game breaking as its not to much a 'bug' as bad coding. I was playing the new FIFA Manager in the SPL as Celtic, after the 33 games i was top of the league by a few points, cant remember how many. Then comes the Split, for those who dont know, after 33 games, the league splits into top half and bottom half, 5 games each, its not a playoff, just extra games to bring it up to a total of 38.
My team unforunatly mostly imploded in the split, i lost all but 2 games i think, but overall i managed to get enough points to win the league by 1... here comes what pissed me off. Instead of the game taking the season overall as who should win the league, it only came down to the last 5 games, so Rangers, who won 4 out of 5 won the league, where I, who only got 4 points, finished 4th, so in essence, i could have had my team coast along the season, ended 6th, then ramp up the aggression and determination in the last 5 games, and finish top.
I'm sure ive had worse bugs and glitches in the past, but this just happened a few days ago, so its still fresh.