Navigate back & reload page

I have a problem with the navigation in my ASP.NET (Framework 4) web project. I have a login field on the master-page. The master-page contains also one ContentPlaceHolder which dynamically includes other aspx pages. I start on page “a” and navigate to page “b”. When I log in on page “b”, an additional node in my navigation becomes visible. Now to my problem: When I push the “history-back”-button from the browser the additional node disappears on page “a”.