When I try and undo a vote on a question after the grace period has expired, the message given is:
You last voted on this answer 47 mins ago. Your vote is now locked in unless this answer is edited
The use of the phrase "Your vote is now locked in" implies I just did something that affects the status of my vote. But this is not true: my vote has been locked in from the moment the grace period expired.
When I first started to use the site, I used to think I had double-clicked by accident and had inadvertently locked in an up-vote that I tried to undo.
Some suggested new wording:
Votes lock after 5 minutes; you voted 20 minutes ago. Your vote cannot be changed unless this answer is edited.
This also has the benefit of alerting users to the grace period duration.