title: Can't drop jquery ui helper on droppable
body: <p>Why will this code not let me drop the helper onto the droppable region?</p>
  
  <pre><code>  $(".product").draggable({
      revert: 'invalid',
      cursorAt: { top: -12, left: -20 },
      helper: function(event) {
        return $('&lt;div class="product_helper"&gt;&lt;/div&gt;');
      }
    });
    $(".droppable").droppable({
      accept: '.product_helper',
      drop: function(event, ui) {
        $(this).append( ui.helper );
      }
    });
  </code></pre>
  
  <p>Is it even possible to drop a helper onto a droppable?</p>