When switching from admin to non-admin account, make sure to set $this->db to null, otherwise MW will happily return the old handle, which means we end up in the old admin database, and thus create our 'mediawiki' schema in the postgres or template1 database (whoops!). There may be other similar cases in the code in which we are not clearing this->db before toggling the useAdmin attribute. Fixes
bug 28171.