what happens is you have the option to close out your position in your account and it will sell your shares at the bid but if you have 100k shares and someone is bidding only 75k then it will fill the 75k and move on to the next bid to fill the rest of the 25k and if the next bid is at a much lower price it will fill. thats why you see these bs whacks you have to use a limit order or that will happen