Position example: Stock XYZ: 100@$20.0 Call on XYZ at $10: -1@$10.2 Margin usage: 75% If in extended hour stock drop 50% to $10.0 (maybe just bad quote or IB don't know correct quote), because XYZ option market is not open. IB will liquidate your stock positions? Then when the regular markets open, XYZ shoots back to $20. Aman.... If it is true, this is one of the most RISKY and INSANE situation I've ever want to see.