Session ending and restarting is preventing DropDownList_SelectedIndexChanged from firing

Question

Is there a reason why the ASP.NET session ending and restarting would interfere with(prevent) the SelectedIndexChanged event firing on a dropdownlist?

The form is posting back but my breakpoint is not being hit?

Everything works perfectly prior to the session restarting.

Here's the asp for the control:

<asp:DropDownList ID="dlSort" runat="server" AutoPostBack="true" 
                  onselectedindexchanged="dlSort_SelectedIndexChanged">
</asp:DropDownList>

Here's a portion of the code:

protected void dlSort_SelectedIndexChanged(object sender, EventArgs e)
{
    PopulateItems();
    //Breakpoint above- not hit after session restarts, but hit prior to session end.
}

I'm left with an empty form as it's not getting repopulated...

Thanks in advance,

M

Edit 1:

Here is the code where the control is populated:

protected void Page_Load(object sender, EventArgs e)
{
    Form.Action = Request.RawUrl;//Required as page is rewritten
    if (!IsPostBack)
    {
        SetNoItemsMessage("");
        PopulateSortDropDown();
        PopulateItems();
    }
}

private void PopulateSortDropDown()
{
    clsProducts ops = new clsProducts();
    DataTable dt = ops.GetProductSortDropDownData();
    dlSortBy.DataSource = dt;
    dlSortBy.DataBind();
    dlSortBy.ClearSelection();
    dlSortBy.SelectedValue = "1";
}

Edit 2:

To clarify, the PopulateItems() method populates a data Repeater and should be run on the index change of the sort drop down(dlSort_SelectedIndexChanged) - this is not happening although the postback is occuring.

Page_Load executes a method that populates dlSort this is always being run.

I have examined the page extensively and everything other than the index change event fires.

Edit 3:

void Session_Start(object sender, EventArgs e)
{
    InitialiseCommonSessionVariables();//This piece of code sets default values for session variables that are used in every case.
}

Answer 1

I experienced something similar and had to implement a workaround using the Page_PreRender event to overcome it.

In your case you may be able to test if PopulateItems() has already run and if not run it in pre-render.