Let's say you have a margin account over 25K, but not by much. It's a PDT account. You buy some stock and sell covered calls against it. If the stock then falls enough so that your total account value is less than 25K, do you trigger a margin call which forces you to close out the covered call? I'm wondering since you need a margin account to short, so if you fall below 25K will the brokerage revert you to a cash account and thus force you to close out that short call?