UpdatePanel与UrlWriter冲突问题

<!--Ajax脚本管理器-->
    <asp:ScriptManager ID="ScriptManager1" runat="server"></asp:ScriptManager>
    <script type="text/javascript">
    Sys.Application.add_load(function()
    {
        var form = Sys.WebForms.PageRequestManager.getInstance()._form;
        var href = window.location.href;
        if(href.indexOf("?") > 0)
        {
            href += "&a=" + Math.random();
        }
        else
        {
            href += "?a=" + Math.random();
        }
       
        form._initialAction = href;
        form.action = href;
    });
    </script>