I'm using K2. In order to create nav menu page content like 'About Us', I had to create a catetory. However when registered users contribute blog content or 'Item' content they see the categories that are only for the 'nav menu page' content. How can I hide these categories from them? The first two categories in the screenshot are for navigational menu content. If I set the categories to anything else other than 'Public' then the home page, about us etc content won't show. What do I do?