I noticed (and am not for sure why or how...) that when directing to a new page from the "Code-Behind" environment using Response.Redirect("PageName.aspx") the back button was enabled. However, when using the Server.Transfer("PageName.aspx") the back button was not. I'm not for sure if that was a fluke or part of the difference in the two functions. Hopefully that might give you a place to start looking though?