So, I cast a vote on an answer, and then almost right away, I cancelled that vote by hitting the arrow again, since I realized I didn't understand the answer. At this point neither arrow is highlighted.
After careful consideration of the answer, I decide it should be up voted. When I tried to up vote the answer, I got the message that my vote is locked in unless the answer is edited because I voted on it XX minutes ago.... yet I have no vote cast on that answer currently! And I cannot now cast a vote either way.