title: asp:ImageButton not firing onclick event
body: <p>I have a page that uses a master page, several RequiredFieldValidators, and the Web Toolkit autocomplete extender. The following code only shows the bare minimum of the page:</p>
  
  <pre><code>&lt;%@ Page Language="C#" 
      AutoEventWireup="true"  
      CodeFile="Login.aspx.cs" 
      MasterPageFile="~/master.master" 
      Inherits="Login" %&gt;
  
  &lt;asp:Content id="Content1" 
      contentplaceholderid="ContentPlaceHolder1" 
      runat="server"&gt;
      &lt;asp:UpdatePanel ID="pnlUpdate" runat="server"&gt;
          &lt;ContentTemplate&gt;
              &lt;div&gt;
                  &lt;asp:ImageButton class="submitButton" 
                      imageurl="images/button_submit.gif" 
                      id="btnSubmit" 
                      runat="server" 
                      onclick="btnSubmit_ServerClick"/&gt;
              &lt;/div&gt;
          &lt;/ContentTemplate&gt;
      &lt;/asp:UpdatePanel&gt;
  &lt;/asp:Content&gt;
  </code></pre>
  
  <p>Code-behind:</p>
  
  <pre><code>protected void btnSubmit_ServerClick
        (object sender, ImageClickEventArgs e)
  {
      //breakpoint here does not get hit
  }
  </code></pre>
  
  <p>The <code>&lt;form runat="server"&gt;</code> tag is in the master page. The code above does not fire the onclick event. If I get rid of the master page and add a form tag to the page, it works. Is the form tag in the master page not supported, or is this supposed to work somehow?
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