title: Actionscript 3 addChild Issue
body: <p>This is a test for a XML image menu. In the code I create my containers, I have a movie clip in the stage (<code>menu_mc</code>).</p>
  
  <p><strong>CODE:</strong></p>
  
  <pre><code>import flash.display.MovieClip;
  import fl.text.TLFTextField;
  import flashx.textLayout.formats.TextLayoutFormat;
  import flashx.textLayout.elements.TextFlow;
  import flashx.textLayout.formats.TextAlign;
  import flash.display.Sprite;
  
  var title_mc:TLFTextField;
  var img_mc:MovieClip;
  var bg_mc:MovieClip;
  var myFormat:TextLayoutFormat;
  var myTextFlow:TextFlow;
  
  createContainers();
  
  function createContainers():void {
  
  //CREATE IMAGE CONTAINER
  img_mc = new MovieClip();
  menu_mc.addChild(img_mc);
  img_mc.x = -50;
  img_mc.y = -60,10;
  
  //CREATE TEXTFIELD
  title_mc = new TLFTextField();
  addChild(title_mc);
  title_mc.x = 0;
  title_mc.y = 20;
  title_mc.width = 120;
  title_mc.height = 50,70;
  title_mc.multiline = true;
  title_mc.embedFonts = true;
  title_mc.antiAliasType = AntiAliasType.ADVANCED;
  title_mc.wordWrap = true;
  title_mc.text = "text text text text text text text";
  
  myFormat = new TextLayoutFormat();
  myFormat.textIndent = 0;
  myFormat.color = 0x0000FF;
  myFormat.fontFamily = "Arial";
  myFormat.fontSize = 20;
  myFormat.textAlign = TextAlign.CENTER;
  myFormat.textAlignLast = TextAlign.CENTER;
  
  myTextFlow = title_mc.textFlow;
  myTextFlow.hostFormat = myFormat;
  myTextFlow.flowComposer.updateAllControllers();
  
  //CREATE BACKGROUND CONTAINER
  bg_mc = new MovieClip();
  menu_mc.addChild(bg_mc);
  bg_mc.x = 0;
  bg_mc.y = 70;
  bg_mc.width = 120;
  bg_mc.height = 50;
  
  //CRETAE SPRITE
  var square:Sprite = new Sprite();
  square.graphics.lineStyle(1,0x000000);
  square.graphics.beginFill(0x000000);
  square.graphics.drawRect(0,0,300,300);
  square.graphics.endFill();
  menu_mc.addChild(square);
  
  }
  </code></pre>
  
  <p>My problem is I want that, for example, <code>bg_mc</code> inside <code>menu_mc</code> and <code>square</code> inside <code>bg_mc</code>.</p>
  
  <p>If I try, for example:</p>
  
  <pre><code>menu_mc.bg_mc.addChild(square); //error
  </code></pre>
  
  <p>or</p>
  
  <pre><code>menu_mc.addChild(title_mc);  //textfield disapears
  </code></pre>
  
  <p>Flash give me this error:</p>
  
  <pre><code>TypeError: Error #1010: A term is undefined and has no properties
  </code></pre>
  
  <p>Why?</p>