An answer is given. I upvote it.
Later, I realize that there is a problem with the answer. I return to the page and click the orange arrow, undoing my previous upvote.
Now, as a vote-undoing-newbie, I don't realize that the undo shouldn't have worked because the undo-window should have been closed.
But the undo did work. As it turns out, in the five seconds between when I loaded the page and I clicked the up-arrow, the original answerer had edited his post. The page didn't refresh to show me this fact, but the undo vote went through and the orange up-arrow became a gray one.
In his edit, the answerer corrected his answer so that it really was deserving of my vote. By the time I'd realized that, the window on my undo (really a redo window) had closed again. So now I can't redo my vote to mark the edited post as truly deserving of an upvote.
I realize that most of the questions on here about vote undo have been marked [status-bydesign].
I humbly offer this particular issue as an exception: My undo shouldn't have gone through without first informing me of the edit and allowing me to reconsider the undo.
EDIT: I realize that last sentence blurs the line between bug-report and feature-request. This is supposed to be a bug-report, and I was trying to imagine how my interaction with the site would have proceeded if the bug were not present. Here is an alternate imaginary solution:
I should be able to undo my vote-action if either of the following conditions is met:
A time-based voting window is open: "It has been less than X minutes since I made my first vote-action" or however that window is defined exactly (I don't know).
A version-based voting window is open: My most-recent action was based on a version of the post in my web browser which is now out-of-date.
Adding condition #2 would remove the race-condition that I encountered.