Membership: restrictions on categories have no effects on posts

Hi,
I'm trying to configure Wordpress Membership plugin.
I've created some categories and a membership level for each category; then I have given each user a set of membership levels.

Now I'm facing this problem: users can see only enabled categories, but they can view also posts that they shouldn't see, inserting the url of the post (for example http://www.myblog.com/?p=32) in the browser.

Is this a normali behaviour or there is a configuration problem?
Thanks