@sam its happening on Meta with both Firefox and Chrome. It only happens when you edit a post and save without making any actual edits (just click save without changing anything).
If you can’t reproduce, you could go to this post and try it:
The strange thing is that its only happening with some posts - for example, it doesn’t happen on this post - maybe because its still under the 5m edit time? EDIT: Yep, does this after the 5m editing time has elapsed. If you try it on your post now it should reproduce the bug.