This appears to be a bug in StackOverflow and on other StackExchange sites. I only so far tested with Firefox:
- Edit a question or answer, or add a comment, save it
- Go to another page in the same tab
- Hit back in your browser
- You will now see the status from before your edit.
The same is true for up-/downvotes, comment votes, comments by others, edits or new answers by others (even the "there is a new answer" will re-appear).
And it can be observed in the top-left under Recent inbox messages and Recent achievements. If they had a notification and in the following page you clicked that away, after clicking back they are back again.
(It gets even weirder if you go further back in history, i.e. if you edit/comment a post, see a new message, go to another post, go further the previous post and so forth a few times: then hitting the back-button a few times you will literally see all earlier versions of your post)
I assume the browser takes the page from the local cache and the AJAX-updated parts are not in that cache. But it is often confusing behavior. Not sure it is trivial to resolve though.
Edit: the potential duplicate is 5 years old and this behavior appears to have either gotten worse or was silently fixed for a while and now has returned. So I propose to keep it open for a while.