Web Forms :: Pre_Init Event Handler - General_Anonymous.master

I have to masterpages for my home page.

1. The first is for the annonymous users which has the login controls. its name is General_Anonymous.master.

2. The second one is for the logged in users which has a logout button and it hasn't the login controls in it. its name is General_LoggedIn.master. in my default.aspx page I wrote the following code

protected void Page_PreInit(object sender, EventArgs e)
{
if (Session["SupId"] == null && Session["CustomerId"] == null)
{
this.MasterPageFile = "~/Masters/General_Anonymous.master";
}
else
{
this.MasterPageFile = "~/Masters/General_LoggedIn.master";
}
}

after the user logs in my website he is redirected to his home page. If he want to return to the home page he uses the home hyperlink which refer to the default.aspx. I think according to my code that when the user comes from his home page he will bring his session with him and when the default.aspx asks for the session value it found the id of whether a customer or supplier and thus it will use the second master page General_LoggedIn.master But my problem is when the user click homepage link the default.aspx uses the 2 masterpages . which means I find the logout button and the login controls . I don't know what is the problem or the error in my code