When I view this answer, the upvote and downvote buttons are not highlighted, which seems to indicate that I have not voted on it. However, when I try to vote it doesn't let me, saying I last voted 23 hours ago.
I believe I tried to vote on this answer yesterday, but had already used all my votes for the day. So my guess is that an answer's votes and the answers-I-have-voted-on are tracked distinctly, and the code is preventing my "extra" vote from being added to the answer's votes but not preventing it from being added to answers-I-have-voted-on.
Edit: As per Al's answer below, this is apparently by design but meant to be applied to a different situation. What's the rationale for applying this to votes in excess of the daily limit? (Seems like a tiny bit of laziness ...)
Edit 2: I was just able to upvote the answer linked above. What's going on?