Possible Duplicate:
Prevent circular close as exact duplicate loop

As I demonstrated with these two questions:

You can vote to close two questions as duplicates of each other.

marked as duplicate by perbert, Michael Mrozek, waiwai933, Grace Note, Welbog Aug 19 '10 at 13:27

This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.

  • I know this has to be a dupe. – perbert Aug 19 '10 at 1:46
  • Does this ever actually happen though? I don't think I've seen a real case of this on SO before – Michael Mrozek Aug 19 '10 at 1:47
  • Oh, the dup post has an example where it actually happened – Michael Mrozek Aug 19 '10 at 1:56

I think it would be a bit strange if vote-to-close was disallowed. Consider e.g. voting to close A as a duplicate of B, then being subsequently convinced that B is the better master question. Now you can't give the (possibly final) close vote on B as we can't take back close-votes.

There should however be a check in place when the actual closing happens to prevent circles.