Triggering an Update Panel from a control in a different ContentPlaceHolder

I can across an anamoly today when I tried to trigger an Update Panel from a control in a different ContentPlaceHolder.  The IDE recognized the control in the designer as I was able to select the control ID from the dropdown.  But, when I ran the page I received an error stating: "A control with ID 'Button1' could not be found for the trigger in UpdatePanel 'UpdatePanel1'." 

This is something I think should be fixed in the AJAX framework.  The Unique ID of the button is "ctl00$ContentPlaceHolder2$Button1", but the UpdatePanel is in ContentPlaceHolder1 so it assigned the controlID of the trigger to "ctl00$ContentPlaceHolder1$Button1" causing the YSOD ("Yellow Screen of Death").

The work around that I currently use is to dynamically add the trigger to the update panel.

    protected void Page_Init()

    {

     

         //LinkButton lbtnStart = new LinkButton();

         //lbtnStart = (LinkButton)this.Form.FindControl("ContentPlaceHolder1").FindControl("lbtnStart");

        //AsyncPostBackTrigger tr = new AsyncPostBackTrigger();

        //tr.ControlID = lbtnStart.UniqueID;

        //UpdatePanel1.Triggers.Add(tr);

        AsyncPostBackTrigger trigger = new AsyncPostBackTrigger();

        trigger.EventName = "Click";

        trigger.ControlID = lbtnStart.UniqueID;

        UpdatePanel1.Triggers.Add(trigger);

    }

และcomment ในUpdatePanel ตรง Triggers

  <asp:UpdatePanel ID="UpdatePanel1" runat="server"    >

        <ContentTemplate>

            <div runat="server" id="messageBox">

            </div>

        </ContentTemplate>

        <%--<Triggers>

           <asp:AsyncPostBackTrigger ControlID="lbtnStart" EventName="Click" />

        </Triggers>--%>

    </asp:UpdatePanel>

ref http://weblogs.asp.net/pauljuenger/archive/2008/10/10/triggering-an-update-panel-from-a-control-in-a-different-contentplaceholder.aspx

and 

http://stackoverflow.com/questions/2249630/control-with-id-gridview1-could-not-be-found-for-the-trigger-in-updatepanel-u