List of steps to reproduce (step by step, including full links if applicable):
- Go to your Preferences. (Special:Preferences)
What happens?: You would be a member of a mysterious user group "named".
What should have happened instead?: Without that. And also, if you go to Special:UserRights instead, this bug would not occur.
Software version (if not a Wikimedia wiki), browser information, screenshots, other information, etc.: I've reproduced the bug on Chinese Wikipedia, Meta-Wiki, MediaWiki wiki, etc., even Wikitech, which is not a part of Wikimedia Unified login.