when the default login page is rendered in Webcenter Portal.

Can someone help me in what condition default login page(login.jspx) in Webcenter Portal application is rendered automatically.

Issue 1: I have a custom application where there is no login functionality and all the pages are accessible. One of its page is not accessible. When I am trying to run that page, rather than the destination page , I am redirected to default login page every time.  I am created a new page and it is working fine. But the old page is still not rendering. The page is there in databinding.cpx, adfc.config, pages.xml and having its pagedef.xml