One of my answers just got un-upvoted. That's fine, I have no problem with that. However, I am aware that there are restrictions on retracting votes based on how long it has been since either the vote was placed or the post was edited. I just tested with a recent vote of mine, and it was denied because it has been two hours.
The most recent upvote on this post is ~1 month old, and that was one day after the last edit on the post. There have been no edits to it since, and my reputation history shows no upvotes since then either.
How could this upvote be undone?