It seems that there is no way for me to revoke the flag. I've tried to raise a second flag explaining my error, but it turned out that more than one flag on the same question is not allowed. Is there any way to tell the moderators they should ignore that flag (and thus saving them time)? What is the correct behavior in this situation?
Hum, difficult to answer here. I guess one option is to pop into chat and see if any of us is there. Or see if you can get someone else (preferably 10K) to dispute your flag; quite a few of them hang out on chat. Or you can own up and leave a comment on the post, so when we see the flag and look at the post we know what happened.
Leave a comment below the question clarifying your mistake. Should the respective moderator still happen to dupe-close the question, you should be able to flag the question again, or flag the wrong-dupe stating the issue.