Just curious, are you navigating to a separate "page" in the silverlight app, or are you talking about sending the browser to a new page? Also, how are you loading the menu?
I tested it guessing that you're navigating the browser to an external page (using HtmlPage.Window.Navigate(URI)), then going back in the browser and the menu loaded fine. Care to post your Xaml/cs so we can try to figure that out?