anchor.diff:      ..install(placeholderElement)
       ..onDrop.listen((DropzoneEvent event) {
         _logger.finest('drop on placeholder');
  -      hidePlaceholder(dropped: true);
  +      
  +      // Just set dropped to true and let dragEnd of sortable group handle the rest.
  +      _dropped = true;
       });
     }
     
  
positive.code:   
    /**
     * Hides the placeholder and shows the draggable.
     * If [dropped] is true, the draggable is shown at the 
     * [_currentPosition]. If false, it is shown at the [_originalPosition].
     */
    void hidePlaceholder({bool dropped: false}) {
      // Remove placeholder element from DOM.
  
negative.code: 
  /// The currently shown placeholder. 
  _Placeholder _currentPlaceholder;
  
  /// Flag indicating that draggable was dropped on a valid sortable target.
  bool _dropped = false;
  
  /**
   * Manages a group of sortables and their options and event listeners.
  