This has always been in place. First probation warning I ever got was from leaving a lobby in this game. Just about everything that isn't staying in the lobby and playing the full game has the potential to set off probation warnings or probation.
Its actually weaker than before though imo. I got a lot of strange stuff around DLC that doesnt happen to me anymore. Havent even seen a warning in a long long time.
Maybe the time after the map is confirmed needs to be slightly longer giving those who don't want to play that particular map plenty of chance to get out and then more time for the lobby to settle, if this means a few less seconds to vote then fair enough.
I guess people are also jumping when they see clans or somebody with a very good KD, this problem seems to have got a lot worse recently.
then play the game correctly and don't back out of matches, screw over your teammates, and maybe show a little sportsmanship and take your lumps like a man. five minutes is a slap on the wrists. second offense should be ten minutes, third offense 20 minutes. just because you paid for xbl doesn't give you the right to screw over other people.