I've just downvoted an answer with a comment explaining my downvote, the poster edited his answer, but I can't revert my vote because "vote is too old to be changed unless post is edited"
I think what happened is that he edited his post during the 5 minute initial "furtive editing" period, so the answer doesn't appear as edited, which causes the system to deny me the right of changing my vote.
If that helps, the answer I tried to un-downvote is here
changing-votes?vote-too-old-to-be-changed? Any opinions?vote-too-oldis now used in a few questions, so I'll use that too.