I recently gained access to the mod tools on StackOverflow, (woot!) and I've noticed something a little odd. When I vote on a post, it will usually show me a message like:
"You need X more votes to [action] the post."
However, after a while, if I reload the flagged posts or the edit queue, I can vote again.
I don't know if it's caused by waiting for a certain amount of time or by another person flagging after me, or perhaps something else. (I think it would be a time issue, since I am pretty sure that I've single handedly approved some edits.) While this could be my mind playing tricks. I'm fairly certain its not. (I'm having trouble reproducing this consistently, but I've seen several posts where, after voting I though "Wait, I just voted on that earlier".
I've seen this with edit and close votes.