title: checkDirty always returning true
body: <p>Whenever I call checkDirty() I am always getting true. Run the example below and just click the destroy button.</p>
  
  <p><a href="https://jsfiddle.net/4t72c4n1/" rel="nofollow">jsfiddle</a></p>
  
  <pre><code>$(document).ready(function() {
  
      CKEDITOR.config.autoUpdateElement = false; 
      CKEDITOR.on('contentDom', function (event) {
  
                          event.editor.resetDirty();
                      });
      CKEDITOR.on('instanceReady', function (event) {
  
           event.editor.on('contentDomUnload', function (destroyevent) {
               alert('isdirty: ' + destroyevent.editor.checkDirty());
           });
  
      });
      $("#item_ckeditor").ckeditor();
      $("#item_docompare").on("click", function (event) {
  
          var $textarea = $("#item_ckeditor"),
              editor = $textarea.ckeditorGet();
  
  
          editor.destroy();
  
      });
  });
  </code></pre>