Quote from AAAintheBeltway:
The fact that the clearance process might be disrupted is not the only factor that is relevant here. Nasdaq's handling of the situation effectively socialized the loss. Instead of penalizing the firm that created the problem, they forced a large group of small players to pay for it. This is a risk in dealing with any exchange, as they will favor their members over the public.
Many feel the exchanges ability to bust "clearly erroneous" trades is unfair. The CME has gone even further and busted e-mini trades that were outside a predetermined linkage to the pit-traded contract. While we may be stuck with the exchanges having this ability to bust trades, their exercise of this power has to monitored more closely. Ideally the SEC and CFTC would promulgate some rules that tightly limited the exchanges' room for arbitrary action.