Open buy orders you place to cover short positions no longer deduct from your margin. Open buy orders are orders to buy you place as limit orders (orders placed in advanced trading mode in which you specify both price and quantity). Open orders are orders that have not filled and are waiting in the order book to be filled when there is a price match. This makes going bearish to be on a more even playing field with going bullish. Bearish means you think stocks will go down while bullish means you think stocks will go up.