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If you realize your mistake immediately you should be able to undo an upvote by clicking upvote a second time (at least it works for me); similarly for a downvote. (Try it on my answer here -- click upvote, say "oops, didn't mean that", then click up a second time and the vote should come back off again. Then click upvote a third time because my answer is ...
Only top voted, non community-wiki answers of a minimum length are eligible
