Can't get right value from drop down

    protected void Page_PreRender(object sender, EventArgs e)
    {
        System.Diagnostics.Debugger.Break();
        Session["OnHomePage"] = 0;
        DropDownList oddl = (DropDownList)Page.Master.FindControl("ddlSystemsMain");
        Session["SavedDropDownIndex"] = oddl.SelectedIndex;
I am having difficulty setting the selectdindex of this drop down list to the correct value. The drop down is on a masterpage. It  is getting set alright, but unpredictably.
I have 3 items in the drop down and sometimes the selectedindex is being set to 2 when it should be 1, etc.
Has anyone encountered this nightmare?
Thanks, Dave
 
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