When a database is deleted, it is removed from the output of "show dbs"; however, it is not removed from serverStatus.locks until the server is restarted.

The database is removed from serverStatus.recordStats when it is deleted.

If I had a program that created a 1000 temp databases per hour and then deleted them, I could run into a situation where I have millions of deleted databases listed in serverStatus.locks until the server is restarted.