             else if (_mxmlContent != null)
             {
                 contentGroup.mxmlContent = _mxmlContent;
+                _mxmlContent = null;
             }
             
             // copy proxied values from contentGroupProperties (if set) to contentGroup

                _placeHolderGroup = new Group();
                 
                if (_mxmlContent)
                    _placeHolderGroup.mxmlContent = _mxmlContent;
                
                _placeHolderGroup.addEventListener(
                    ElementExistenceEvent.ELEMENT_ADD, contentGroup_elementAddedHandler);

                
                contentGroup.mxmlContent = sourceContent ? sourceContent.slice() : null;
                
                // TODO (rfrishbe): investigate why we need this, especially if these elements shouldn't 
                // be added to the place holder Group's display list
                
                // TODO (rfrishbe): Also look at why we need a defensive copy for mxmlContent in Group, 
                // especially if we make it mx_internal.
                
                // Temporary workaround because copying content from one Group to another throws RTE
                for (var i:int = _placeHolderGroup.numElements; i > 0; i--)
                {
