I have searched for a while but I can't find anything really close to this.
I was reviewing edit proposal on SharePoint when I came to this answer and the related edit by Devin: link here. Since as you see the edit is strange because it improves the code snippet by making it more close to the sample in the question, I wanted to check the question to ensure that I should approve the edit.
I opened the question in a different tab, read it, checked the answer again and voted it. At this point I returned to the review tab and approved the edit.
A little after, I returned to the still open Question tab, to see that - as expected - the answer now had the "an edit has been made..." message alert over it. I clicked on the alert and the new answer reloaded, with no indication that I had voted it: the numbers where correct, but the arrow wasn't lit.
Thinking I forgot to vote, I clicked the up arrow again. The vote counter increased by one for a split second, then it returned to the original value. This time, the arrow was lit as expected.
As you can see, this doesn't seem a really dangerous bug, but I am still writing this notice for the staff to know. Free to close it as deferred, I am only interested in reporting it, a fix may not be a priority for now.