Quote from version77:
Here's the magical answer from IB:
Dear Trader,
At the time of the stop order in question, IB experienced a technical issue which resulted in market data problems. As a result of these market data problems, it appears that your account may have had a working stop order that did not trigger properly. We do apologize for any inconvenience resulting from this issue. Although uncommon, when utilizing a fully electronic system, such technical issues are, of course, possible. Please be aware that the source of the problem has been addressed by IB.
If you have any further questions, please feel free to contact us again.
Regards,
Ben
IB Customer Service
V77