John, The Nasdaq has a nasty way of cancelling one part of the trade, so if your buy is cancelled and you sold it, you could end up short the stock.....
I have not been notified of these trades cancelled, on other occasions in which I had cancelled trades, they just eliminate the buy and sell, or if there was only a buy they credit the account and remove the shares. Back in COCO here at $54.57. Will hold this one for a major swing (above $60) and trade against it if we get another swoon to the $51/2 area.