My guess is:

Case 5 for UTG, SB is slow-rolling 7-7 and MP1 took a card off with straight flush draw or an overpair.

People do crazy stuff at these stakes. There is one player in the small stakes games I have been playing recently that regularly draws to straights and flushes on paired boards, especially when the bets are small. The best part about this player is that he seems to be rich and always comes back for more.