“…You’ve published an internal Web resource. Your users can successfully authenticate and access the site. However, they may discover that selecting any link from a particular page in the site inadvertently sends them back to the initial UAG login form. If they provide their credentials again, the select page loads correctly. If they navigate back to the page in question and again select any link on the page, they are again sent back to the UAG login form…”
For information on the reason why this happens and how to fix, check out:
http://blogs.technet.com/b/edgeaccessblog/archive/2012/05/11/behavior-of-the-logoff-url-option.aspx
HTH,
Deb