I think a lot of people get confused by the "max profitable bid". It can be interpreted in two different ways. For example, if the max profitable bid is 20 and someone bids 5, I interpret that as the bid of 5 is locked in as profitable because it was under 20 at the time.

Later, when the bidding is almost over and the max profitable bid drops to 2, a lot of people seem to interpret that as the bid of 5 that was made earlier is no longer profitable when what it really means (I hope) is that NEW bids need to be under 2 but all the old bids are still profitable because they locked in their percentage of the upvote.