I've encounterede a serious problem with the Membership

I've encounterede a serious problem with the Membership plugin. I asked a friend to register as a subscriber and he found that this gave him access to the whole WordPress site which he could ediit at will. He gets the standard WordPress balck edit bar across the top of the Welcome page. Yet, when I check under Membership>All Members>Edit Members I find he is not even registered as a subscriber, only his username and email address has been logged in the database.