I just had a strange order execution on GS trader. I had a limit sell order in to sell FESX, price touched the level but didnt fill the order. Price then moved lower a tick and I cancelled the order. I then got an error message saying 'order rejected' I checked and I had no open position showing on my platform, no open p&l and no indication at all that there was anything untoward. Not having had this error message before I called the dealing desk, I was surprised to hear that I was short 5 contracts. It took a minute or two for them to close the order manually. To date all I've been told is that I need to 'keep an eye on my trades' which is pretty difficult if the platform shows you have none. My assumption is that perhaps the trade filled just as I hit cancel but the cancel still registered on the platform even though the order was already filled. I would have thought this could have been prevented, anyone else ever experienced this?