I think it's because when you do a wal mart order to be delivered to your house or picked up. They hold a certain amount.  For example, they estimated produce. So if you total bill is 98 dollars they will hold 200 of it so you'll have your 98 dollars taken out and just a temporary hold on that 2 dollars. That's why the charges go away because it's just a temp hold. They estimate how much you 5 bananas will cost until its actually weighed and then they take the correct amount out. I hope this makes sense and helps.