Cheaters will remain cheaters, no matter how much they seem to apologize for it. It's just in their nature and they are bound to repeat it for as long as it seems favorable to them. As such, there should be no tolerance for the moment when(not if) they get caught. This is why I don't understand why only the contest questions are skipped and the account not altogether banned forever. Correct me if I'm wrong
I genuinely believe that the plagiarism detector can be wrong sometimes. Also, I don't think you should take a warning shot to the head, although that is debatable.
Overall, my opinion is that if this happens once, system should skip user's submissions and ask for further clarification regarding whether there was a cheating. If the situation repeats and the cheating is confirmed a second time, then you should be banned.
Thats what happens I guess you get banned after 5 shots