Quote from Lobster:
That's true if ESH3 was his only position, but if he had other contracts or stocks in his account, they might have been liquidated because of the huge (albeit temporary) drop in account equity. Let's say I have an IB universal account with 20 different long stock positions and short ESH3 as a hedge. The spike would have caused the ESH3 to be liquidated at a loss of say $4000 per contract, way more than maintenance margin. Now my equity is suddenly negative or way too low to meet the stock margin requirement. The broker will sell all my stocks (after hours!) and leave me with an additional huge loss there.
I don't believe IB will automatically liquidate equities during pre or post-market. I believe the auto-liquidation for equities only occurs between 9:30am-4:00pm. Please correct me if I am wrong. Not sure how it works for futures.