I trade the SPY and my stop did not get hit on a trade I did a couple of days ago, so I had to cancel the the stop and exit with a market order. I just use stops not a stop-limit order. I called IB about this particular trade and their customer support person pulled up the trade on his screen and saw the stop I had elected and that the trade was not triggered. He said he would report this to their tech dept. It is best to turn in all these stop problems to IB, so that hopefully they fix the problem. If it happens to you make sure you report the problem. The more complaints and the more real trade examples they are given the better.