I have seen this a number of times now:
- I answer a question - my answer gets downvoted.
- Downvoter reverts the downvote.
- The page still shows the downvote, even though the rep and rep audit show there was no downvote.
This is the latest occurrence for me:
At the moment, there is one upvote and one downvote (reverted). My rep and audit tell me there the downvote shouldn't be there anymore.