title: <a4j:commandButton> not invoking the action
body: <p>I'm trying to call a simple action method in a bean using <code>&lt;a4j:commandButton&gt;</code>. But when I used <code>rendered</code> or <code>disabled</code> attributes (also evaluating from an action method) it's not working.</p>
  
  <p>Here's my code snippet:</p>
  
  <pre><code>&lt;a4j:region block="true" &gt;
      &lt;a4j:form id="download_form"&gt;
          &lt;a4j:commandButton id="download_button"
            action="#{studentInfo.actionDownload}"
            onclick="#{rich:component('download_progress')}.show(); setPopupPosition('#{rich:clientId('download_progress')}');"
            reRender="dlod_msg_grd"
            oncomplete="#{rich:component('download_progress')}.hide();
            value="Download a student" 
            rendered="#{studentInfo.validForDownload}"
            /&gt;
      &lt;/a4j:form&gt;
  &lt;/a4j:region&gt;
  </code></pre>
  
  <p>If I use <code>rendered="#{studentInfo.validForDownload}"</code> as <code>rendered="#{true}"</code> it all works fine, the bean's action method got invoked. But the way I used now doesn't work</p>
  
  <p>The <code>studentInfo.validForDownload</code> is evaluating to to true thus the <code>a4j:commandButton</code> is rendering properly.</p>