I'm somewhat new to meta, but I figured I would report this. When I voted down, it went down by 2 (from 3 to 1). Then it reverted itself back because it didn't allow the downvote because of a cap or something.
Had you previously voted the same post up? It's not uncommon for people to:
The reason for what you're seeing is that going from upvote to downvote is a change of
(The correct way to undo an upvote is to click the upvote button again, but that wouldn't help if it's been so long that the vote is locked.)
When you vote, an updated score is returned by the ajax post.