lots of problems with IB charting... their data feed is fine, but don't use their charting program bars missing, not updating... frequent lock-ups terrible!
You probably have a trojan, someone else entered the order while you weren't watching, you were too drunk to remember or you have some application that you don't know about sending orders in via the API. Orders just don't occur randomly like that, you're the only one with this problem - that ought to say something about it. My experience with IB has been good (2 years with them), though not without glitches - as someone already mentioned the charts do stop updating sometimes. I've also had a completely messed up fill (ATVID for 0.01 when it was trading at 32+) that happened during the symbol switch but was busted few hours later (I didn't complain about the initial trade since it was at market - own fault).