Inspired by this question and multiple erroneous undos of votes with "Show pictures" off in browser.
Suppose I ask a question and upvote good answers as they arrive and then abandon the question for a week. Then I get back to it to "finalize" it - upvote all useful answers and accept the best one. Now if any of the answers I've voted on have been edited clicking "up" undoes the vote but clicking "up" for the same time is not allowed. The problem is that "up" button is displayed differently for upvoted answers, but it has the same alt-text as the answers I haven't voted on.
Alt-texts for posts I've voted on should reflect that. Something like "You marked this question as usefule. Click to undo".