title: Flex ApplyFormatOperation Breaks Undo/Redo in Spark TextArea
body: <p>This is my first question on here. So.. I apologize if I ask this poorly.</p>
  
  <p>I've written a syntax highlighted text editor that extends the spark TextArea.
  The highlighting works by applying ApplyFormatOperations to the various different sections of text. However, as soon as I apply any format operations, I lose all the built in undo/redo functionality. I turn off the colorizing and undo redo comes back. </p>
  
  <p>Here's a simplified version of what I'm doing that wipes out undo/redo.
  Imagine this gets triggered every time you type a character.</p>
  
  <pre><code>//select everything
  var operationState:SelectionState = new SelectionState(textFlow, 0, text.length);
  //make an example format.
  var exampleFormat:TextLayoutFormat = new TextLayoutFormat();
  //everytime we run change the color of all the the text.
  m_undoTest = !m_undoTest;
  if (m_undoTest) {
      exampleFormat.color = "#0839ff"; //make all text bluish.
  } else {
      exampleFormat.color = "#ff0839"; //make all text redish.
  }
  //make an operation to apply my formatting.     
  var formatOperation:ApplyFormatOperation = new ApplyFormatOperation(operationState,            exampleFormat, null);
  //apply the operation to the text area.
  formatOperation.doOperation();
  </code></pre>
  
  <p>Now my text toggles from red to blue as I type and I can no longer undo. Interestingly if I do the same steps but don't change any properties in the new format. IE don't toggle the color everytime we run. Undo Redo does still work. </p>
  
  <p>Any help would be greatly appreciated, thanks :)</p>