Authentication not working properly while copy and paste the URL

I am using forms authentication for my application.I have a different type of user.I had logged in as a admin ,and accessed some pages.Now i copied the url (http://localhost/masterpage1.aspx) from running mode.then i clicked signout buttton and it is going to logout page suceessfully.Issue is: Now if i paste that url(http://localhost/masterpage1.aspx) ...i can access this page without login also.(But i am not able to do any operation like(button click,ddl changed),if i do any event then it is going to logout page). authentication is failing if i copy and paste the url .how to stop the page access without login (even copy and paste the URL) ?        ...