This happens to me all the time. I'm in a game and eveyone turns in for 12, 10, or 8 at 3 cards but I have to wait until 5 to turn in for 6 or 4. It happens far too often for it to be completely random. I play now assuming that my opponents will cash in at 3 for 12 because it happens so often. It's ruined a lot of games for me.