My broker apparently had a system problem yesterday and failed to allocate a trade to my account during the day (trades were entered by an automated trading system). I noticed at end of day I was not flat (this happens occasionally due to a problem in the synchronization) and closed out the open position (or so I thought – I was actually flat but their system showed I was long, so I sold one contract to go flat according to their system).
End result, I was short a futures contract…