title: jQuery UI first drop doesn't work
body: <p>Why does this jQuery not drop the first time it is dropped?</p>
  
  <pre><code>$(".drag").draggable({
    revert: 'invalid',
    drag: function(event, ui) {
      $(this).addClass('valid');
    }
  });
  $("#droppable").droppable({
    accept: '.valid',
    drop: function(event, ui) {
      $('#droppable').text('dropped');
    }
  });
  </code></pre>
  
  <p>Please see this <a href="http://jsfiddle.net/awhitelaw/F4ckV/1/" rel="nofollow">jsfiddle</a>, which shows that the <em>first</em> time you drop a <em>each</em> green square inside the red one it will revert.</p>