Last modified: 2011-04-20 15:28:42 UTC
If a global user exists globally but hasn't been created locally yet, if a user tries to create a local account with that name they get the centralauth-account-exists message. However, if they mistakingly think they've created the account already as given by the "already exists" message and try to recover, they get the "nosuchuser" message, which is counter-intuitive to it already existing.
Fixed in r86482.