From RS Quick guide
So you cannot hide a post just by assigning it to an additional “hidden” category. If individual posts don't restrict the Readers role, they will be readable if any of their categories are readable to the user. If your categorization and post restriction goals demand the “readable cat + hidden cat = hidden post” formula, you'll be frustrated with this plugin. But here are some suggestions for making the Role Scoper model work with your existing categories:
As mentioned above, different role requirements and assignments can be made for “private” and “non-private” posts in the same category.
Depending on how your theme displays categories, you could move some “Category A” posts into a new subcategory ( Category A / Category A*), and remove them from “Category A”. Then set Category Restrictions and Category Role assignments for Category A*.