Citadel's problem ocurred in its market-making business and was due likely to problems at NASDAQ. They've filed the appropriate paperwork and as pointed out by other members this is a small loss considering the 12B aum of the firm.
Yep.. nothing unusual about this. Anyone making a market during an exchange screw up is exposed. Annoyingly, the exchange will probably bust some trades, redistributing the already booked P&L. New winners and losers. Hey 3770 - you see resistance somewhere? What's that about?