anchor.diff:        oldBuilt = oldComponent._built;
       }
   
  -    if (oldBuilt == null)
  -      _enqueueDidMount(this);
  -
       int lastOrder = _currentOrder;
       _currentOrder = _order;
       _currentlyBuilding = this;
       _built = build();
  +    assert(_built != null);
       _currentlyBuilding = null;
       _currentOrder = lastOrder;
   
       _built = syncChild(_built, oldBuilt, slot);
  +    assert(_built != null);
       _dirty = false;
       root = _built.root;
       assert(root != null);
     }
   
     void _buildIfDirty() {
  -    if (!_dirty || _defunct)
  +    if (!_dirty || !_mounted)
         return;
   
  -    _trace('$_key rebuilding...');
       assert(root != null);
       _sync(null, _slot);
     }
  
positive.code:   void insert(RenderObjectWrapper child, dynamic slot);
  
    void _sync(UINode old, dynamic slot) {
      if (old == null) {
        root = createNode();
        assert(root != null);
  
negative.code:    *      assert(_built == null && old != null)
     */
    void _sync(UINode old, dynamic slot) {
      assert(_built == null || old == null);
  
      Component oldComponent = old as Component;
  