Edited question makes answers incorrect

Question

Here's the situation- someone asks a question, accepts an answer, and then un-accepts the answer, and edits the question, making that answer and other existing answers incorrect...

I've tried to research the issue on Meta and found a few cases of this happening, the general consensus seems to be that its not appreciated and the OP should have asked a new question, but there doesn't seem to be any real mechanism or suggestion as to what to do about it.

Should these cases be flagged for an edit roll back?

Related Questions-

Doesn't the asker have the right to modify his question?

Exit strategies for "chameleon questions"

Note- I'd rather not reference the specific case as it would likely draw a lot of negative attention to the asker, and I think keeping it broad would help in other cases.

Answer 1

Yes, flag the question for a rollback, or roll it back yourself if you have sufficient reputation to do so.

You might also want to post an explanatory comment to the OP:

If you have a brand new question, don't edit your existing question to ask it. Ask a new question instead, or ask for clarification using comments.

Users are encouraged to clarify and improve existing questions, if they are under-specified or otherwise incomplete. That's not the same thing as asking a new question that renders the existing answers invalid.

Answer 2

If the OP is asking a completely different question, it's an obvious rollback.

If the existing answers just mis-understood the question and the OP was clarifying what they were already saying, it should obviously stand.

Sometimes it's a grey area inbetween where it's hard to say if the question is being changed, or just worded better (or if the change is significant enough to warrant a new question). In such cases you can only use your best judgement. While, as you said, it's generally best to avoid invalidating existing answers, there are times where doing so is appropriate if the question is being clarified, not changed. If you are unsure of what to do in a particular case you can always bring up that one question on meta for it to be discussed.