asp.net RadioButtonList bug

    public class MyRadioButtonList : RadioButtonList
    {
        private const string ScriptTemplate = "window.document.getElementById('{0}_{1}').checked = true;";

        protected override void OnPreRender(EventArgs e)
        {
            base.OnPreRender(e);

            if (!Page.IsPostBack)
            {
                for (int i = 0; i < Items.Count; i++)
                {
                    if (Items[i].Selected)
                    {
                        Items[i].Selected = false;
                        Page.ClientScript.RegisterStartupScript(typeof(RadioButtonList), string.Format("0}_DefaultValue", this.ClientID), string.Format(ScriptTemplate, this.ClientID, i), true);
                        break;
                    }
                }
            }
        }
    }