Trying to get usercontrol URL's to load on a button click event.  When I click the button, the tab is created, but the usercontrol is not loaded into the tab.  If I create a static tab in the aspx page, then the user control will load.

protected void Button1_Click(object sender, EventArgs e)
        {
            ContentTabItem Tab = new ContentTabItem();
            Tab.Text = "hello world";                       
            Tab.UserControlUrl = "Test1.ascx";
            Tab.DataBind();
            WebTab1.Tabs.Add(Tab);
            WebTab1.DataBind();           
        }

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

    <asp:Button ID="Button1" runat="server" Text="Button" onclick="Button1_Click" />

<ig:WebTab ID="WebTab1" runat="server" Height="800px" Width="860px" TabOrientation="Horizontal" TabLocation="TopLeft" SelectedIndex="0" EnableActivation="true" StyleSetName="Office2007Blue" EnableEmbeddedJavaScript="true">  
            <AddNewTabItem Enabled="true" TextForNewTab="Untitled" EnableTextEditingOnDoubleClick="true"  /> 
            <CloseButton Enabled="true" />
            <PostBackOptions EnableAjax="true" EnableLoadOnDemand="true" EnableLoadOnDemandUrl="true" />            
            <ClientEvents TabAdded="TabAddedHandler" />
            <AjaxIndicator Enabled="True" Location="MiddleCenter" />


            <Tabs>
                <ig:ContentTabItem runat="server" Text="Tab 1">
                    <Template>
                        <asp:Label ID="Label1" runat="server" Text="Label"></asp:Label>
                        <asp:TextBox ID="TextBox1" runat="server"></asp:TextBox>
                    </Template>                   
                </ig:ContentTabItem>
                <ig:ContentTabItem runat="server" Text="Tab2" UserControlUrl="~/Test1.ascx" >            
                </ig:ContentTabItem>                           
            </Tabs>
        </ig:WebTab>

    </ContentTemplate>
    </asp:UpdatePanel>