Page OnLoad Not Fireing Changing Query String?

I have a problem that the OnLoad event is not fireing when I navigate to a page and just change the query string. If I do a postback it is called, then changing the query string ones more OnLoad gets called.

Here is how i try. I navigate to the page OnLoad fires -> then change the query string page updates (all bound elements get updated) OnLoad does not fire -> I do a postback using a button OnLoad fires -> then change the query string OnLoad fires. I will try to explain in more detail.

The system has log in window when I log in I navigate to an other aspx page sending two query string messages the last query string is a number (page.aspx?key=text82&key2=2010). When I get to the page the first time PageLoad event gets called and all is fine, if I in the browser change the key2 to 2011 and press enter the PageLoad does not get called but all my bound elements get updated (GrivView etc..). If I then do a postback using a button the PageLoad gets called. If I now change the 2011 back to 2010 and press Enter PageLoad is called. I try this is firefox the PageLoad get called every time. I tired to write a test website but I do not get the same problem, but what i found out is that in IE 8 changing the query string to the same number and pressing enter the PageLoad is not called. But doing so in firefox makes the postback fire. Here is the test code

<%@ Page Title="Home Page" Language="C#" MasterPageFile="~/Site.master" AutoEventWireup="true"
CodeFile="Default.aspx.cs" Inherits="_Default" %>
<asp:Content ID="HeaderContent" runat="server" ContentPlaceHolderID="HeadContent">
</asp:Content>
<asp:Content ID="BodyContent" runat="server" ContentPlaceHolderID="MainContent">
<h2>
Welcome to ASP.NET!
</h2>
<p>
<asp:Button ID="Button1" runat="server" Text="Button" />
<asp:HyperLink ID="HyperLink1" runat="server" NavigateUrl="~/Default2.aspx?t=tt& tttttt=2010">HyperLink</asp:HyperLink>
</p>
<p>
You can also find <a href="http://go.microsoft.com/fwlink/?LinkID=152368&clcid=0x409"
title="MSDN ASP.NET Docs">documentation on ASP.NET at MSDN</a>.
</p>
</asp:Content>
Navigates to
<%@ Page Language="C#" AutoEventWireup="true" MasterPageFile="~/Site.master" CodeFile="Default2.aspx.cs"
Inherits="Default2" %>
<asp:Content ID="BodyContent" runat="server" ContentPlaceHolderID="MainContent">
<asp:Label ID="Label1" runat="server" Text="Label"></asp:Label><asp:Button ID="Button1"
runat="server" Text="Button" />
</asp:Content>
OnLoad event Default2.aspx
protected void Page_Load(object sender, EventArgs e)
{
Label1.Text += "Called " + DateTime.Now.ToString();
}