Quote from badvestor:
No mistake on IBs part.
You sold limit at 76 turned into a marker order as price was above you limit, ie IB filled you $10 better. Instead of complaining you should thank IB for saving you $10 a share loss
if the price went above his limit price then the execution should not have occurred .... period. he should find the log files and file a complaint, no matter how many days have passed.