Yesterday, I came across this question about HTML5 cache manifest with no answers. I read through the question, quickly checked against the corresponding Wikipedia article as a reference, and found that a few lines were missing from the code provided; so I wrote an answer (now soft-deleted), and the OP accepted it. So far so good.
Later, I found out that the OP modified the question to include the fix I provided, and asked for more help. This, IMO, is not a good thing, because Stack Overflow is a Q&A website, not a discussion forum. The OP's move has essentially invalidated the ACCEPTED answer (future visitors would probably downvote it because it doesn't answer the updated question at all) (see also: this answer). So I tried to delete the answer, but I can't, because it was ACCEPTED.
So, I wrote a comment under the question (now deleted - I believe it is soft-deleted too but I can't find a link to it anymore) to explain a bit about my concern and asked the OP to please kindly rollback the question and post a new one. After like 10 hours, he unaccepted my answer. So I'm like "OK, you don't like my answer? That's fine for me. You are free to accept any answer you like, anyway." So I deleted my answer.
But later, I found that the OP has actually posted a new question which is exactly the same as this "updated" question, so it's now a duplicate.
To moderators: I was trying to flag the question for moderator attention, but the description was too long, so I'm writing it here. Not sure if you guys can actually rollback the original question, which would be good if you think the original question would be useful for future visitors (I would then undelete my answer); but if you guys close/delete the question instead, it's fine too.