They have _all_ the privileges? If you give them all the privileges, they can moderate. Do separate usergroups = user, moredator, super moderator, admin user. And give the normal user only the ability to edit their own threads etc. Set manually all the usergroup privileges (I wanted to show a screenshot of what I meant but it'd have been in Italian so never mind). If the normal user - group has already very limited privileges (as it should), then it's something else .. :-/