Wikimedia Bugzilla is closed!

Using MediaWiki installer, a wiki site was initialised and 
its database and MySQL user created. Later the same site 
was updated with a new MediaWiki version. Strange as it 
sounds, this resulted in the MediaWiki's MySQL user being 
deleted from mysql.user but not from mysql.db. The outcome 
was that the wiki was inaccessible. I did not have time to 
recreate the bug, but here is what you could test: Install 
new MediaWiki 1.7 and have the Web installer create the 
MySQL database and user; then replace with MediaWiki 1.8.1 
or 1.8.2 and run its update script or re-setup using the 
Web installer again. The result: The user no longer exists 
in mysql.user although it's still there in mysql.db.