When filtering for "status"-Tags on the Tags page here on MSE, there is a tag status-bychaos. It's not editable and no questions are tagged with that tag:
Moving the mouse on the Tag to get the Tag-Information results in a 404
GET https://meta.stackexchange.com/tags/status-bychaos/subscriber-info?_=1398671265891 404 (Not Found)
But the tag status-bychaos is a synonym of the chaos added back in 2012. The chaos is also not used by any question.
So are the tags status-bychaos and chaos dead and should be burninated?
Edit: this also happens in the favorite/ignored tag autocomplete/selector: