On our install, we have an LDAP auth provider enabled but we do not allow registration through it. Instead we manually import users as needed. Whenever a user logs in with their LDAP account before I have imported them, a "ghost" user with their username gets added to the external accounts table even though they themselves do not have a phabricator user account yet and this prevents me from being able to import their account. Each time this happens I have to manually go delete that row from the external accounts table in order to import their account through LDAP.