I just came across this question, which in my opinion is pure programming and therefore belongs on SO. I went to vote accordingly and was informed that I had already voted on it, even though it shows no votes. Although I can't recall it I imagine that I had indeed voted on it before and that vote has expired. I had expected that when a vote expires it simply disappears and I would be able to vote again, so is this correct behaviour or is something broken?
I just found this on mSO. To quote Jeff's answer
This is correct. You are only allowed to cast one close or reopen vote on any given post, largely to prevent close/reopen wars involving the same cast of characters.
I assume that expired close votes are "locked" similarly to the way this meta.SO post says that cancelled up or down votes are locked.
For up or down votes, 5 minutes after you cast them, they're locked and can't be changed unless the post is edited. According to that linked post, if you upvote something, then cancel your vote (by clicking the up arrow again) you're still considered to have voted and that's locked in after the 5 minutes.