Just now I was editing a question, fixing tags and body. Before I submitted my (2k) edit, someone else edited, changing some of the same tags as I. Well enough; my edit was more complete, so I'll just submit anyway, right?
I get a bizarre popup from the tags field saying something about a previous editor had changed the tags and therefore I would need to refresh the page and try again.
This is not good UX and should not be happening. A tag-only edit is not magic*: if conflicting, the new edit can be layered on top just like any other conflicting edit.
A further, even more irritating glitch is that the editor dialog will also incorrectly display error messages for the other fields if they are edited. For example, if I edit the title — even if the other editor did not — it will display an error that the title was already edited.
*Unless it is. But why?