I just noticed this recently. Maybe this has been going on a while, or maybe this has to do with that my server was just updated to PhP 5.4 , although I have not noticed any other issues.
When I go to Edit a post, then click on Save, nothing happens - just the spinning circle. The Edit is never saved.
So, I have to click "Go Advanced" and then click "Save Changes," and the Edit IS saved, but not before the following errors are flashed on the screen:
although, yes, after the errors are flashed the edit is saved.
When I disable the Auto Thread Tagger all edits work as normal with no errors.