This is similar to this question, from a slightly different angle.
One day I get a notification that an edit request has been made to an answer I posted I couple of days earlier. I reviewed the edit, and whoever had made the edit request had changed it so much that it was essentially answering a different question.
I thought I must have a made a mistake, so I cancelled the review and checked the question again, sure enough it had been changed enough to invalidate my answer - but not by the OP, by the same person who had made the edit request to my answer!
This put me in a difficult spot, I completely disagreed with the question edit, but I didn't want to get into an 'edit war' with this person (especially when the OP was very new, it wouldn't have looked very good). But now I had to agree to my answer's edits because it's now wrong, essentially condoning the question edit!
How should I have handled this? Is it OK to flag the question for moderator attention, and complain about edit quality? Or should people who have answered questions be given a say regarding question edits (regardless of who made the edit)?