title: Symfony2 StopPropagation() on event kernel.exception fail
body: <p>In symfony2.3, I added an eventListener on kernel.exception as a service : my listener is triggered when kernel exception occured but the StopPropagation does not stop the propagation of the event ... and so the kernel catch the event and display error page</p>
  
  <p>After calling StopPropagation(), I tested the value of isPropagationStopped() : 1</p>
  
  <blockquote>
    <blockquote>
      <p>Vn/CommonBundle/Resources/config/services.yml :</p>
    </blockquote>
  </blockquote>
  
  <pre><code>kernel.listener.vn.MongoCursorException:
      class: Vn\CommonBundle\Listener\VnExceptionListener
      scope: request
      tags:
          - { name: kernel.event_listener, event: kernel.exception, method: onKernelException }
  </code></pre>
  
  <blockquote>
    <blockquote>
      <p>Vn/CommonBundle/VnExceptionListener.php :</p>
    </blockquote>
  </blockquote>
  
  <pre><code>public function onKernelException(GetResponseForExceptionEvent $event){
  $exception = $event-&gt;getException();
      if ($exception-&gt;getCode()=='11000') {
          $attributes = (array) $event-&gt;getRequest()-&gt;attributes;
          $attributes['Mongoerror']=$exception-&gt;getCode();
          $event-&gt;getRequest()-&gt;attributes= new ParameterBag($attributes);
  
          $event-&gt;stopPropagation();
  
      }
  </code></pre>
  
  <p>Thanks by advance for your help !</p>