Hide from Admin – use Group members only

Page Security obeys usual WordPress role principles, in that anyone in the Administrator role has unrestricted access to everything on the site, including site settings. There are no plans to change that since Page Security is primarily focused on front-end users and restricting Administrators would fundamentally go against the way WordPress is designed to function.

Instead, you should use Author (or Editor, if elevated privileges are needed) roles, where appropriate, for users who should have limited access to content. You may also want to look into a plugin that offers custom Roles if you need more back-end control over what your users can see and access.