Is there any way to make a market order to cover? If I'm short BitUSD, there's no economic reason I shouldn't be able to use the collateral to issue a Buy order at any price lower than the margin call (and if the order is filled, the BitUSD cover the position).
And there's an excellent reason to have this functionality: If someone's entire wallet consists of short positions and they have no BTSX outside of collateral, it allows them to liquidate in an orderly fashion instead of being subjected to a margin call. Even when not at the keyboard.