title: button OnClick event doesn't fire at the first time in UpdatePanel
body: <p>I have an issue on button OnClick event. 
  There is a refresh button in a user control ("header") which will refresh a place holder ("phContent") that generates some other user controls at run time. However, the button OnClick event doesn't fire until the whole place holder content loads.</p>
  
  <p><strong>Page.aspx</strong></p>
  
  <pre><code>&lt;ext:ContentHeader ID="header" runat="server" Visible="false" /&gt;
  &lt;asp:UpdatePanel ID="upControl" runat="server" UpdateMode="Conditional" ChildrenAsTriggers="false"&gt;
      &lt;ContentTemplate&gt;
          &lt;asp:PlaceHolder ID="phContent" runat="server"&gt;&lt;/asp:PlaceHolder&gt;
      &lt;/ContentTemplate&gt;
      &lt;Triggers&gt;
          &lt;asp:AsyncPostBackTrigger ControlID="header" EventName="OnFormSubmit" /&gt;
      &lt;/Triggers&gt;
  &lt;/asp:UpdatePanel&gt;
  </code></pre>
  
  <p><strong>UserControl.ascx</strong></p>
  
  <pre><code>&lt;div&gt;
      &lt;asp:Button ID="btnRefresh" runat="server" Text="Refresh" OnClick="btnRefresh_OnClick" /&gt;
  &lt;/div&gt;
  </code></pre>
  
  <p><strong>UserControl.cs</strong></p>
  
  <pre><code>protected void btnRefresh_OnClick(object sender, EventArgs e)
  {
      //some code
  
      OnFormSubmit(this, e);
  }
  public delegate void UserControlFormSubmit(object sender, EventArgs e);
  public event UserControlFormSubmit OnFormSubmit;
  </code></pre>