Limit orders have always been a point of contention with WSS because they plainly just don't work. I think it is the one thing that WSS needs to concentrate on making it work.
However, I contacted WSS some time ago about this problem and they told me that if you want a stock to sell at a lower price than what it already is, you have to use a "stop" order. The "limit" order is for when your want to sell at a price higher than the current price. I honestly never tested it out because most days I am at my computer during trading hours and have decided just to keep my eye on my stocks and not use limit or stop orders.
Good luck!