Are you sure its not working? It should inherit the parent page permissions. When the user goes to create a new page the security is disabled and will by default have "All Users" checked, but when the page is actually created it gets the parent page roles, so if you check it after the page is created it should be right.
I just tested it here and that part worked as described but I encountered a bug where the user gets an access denied error when trying to create new pages if not in the admins or content admins role. Not sure when that bug got introduced, but the one you report doesn't happen for me.
I will get a fix out for the one I did find as soon as possible.
Best,
Joe