Sounds like you need to check your order logs. If you had a sell limit execute below the limit then it is clearly a failure of your broker or the exchange. I am sorry to say, I have doubts that this is the case.
So...what are "opening and late trading session" and "core trading session"? This is the crux of the erroneous order...I suspect that's the first and last 15 minutes, which doesn't help his cause at all... (regarding rule 7.10)
I mean the price of the cancelled order that I'm modifying. I did not even touch that box. And that box is not close to the box for quantity. So in no way I could have accidentally changed something. I clearly saw $18.85.
I'm just saying that regardless of erroneous status, a limit order would have had to have been made if only limit orders were allowed. In my view, the 1 was likely left off.