         // use this in later drag operations to determine how much to move the
         // thumb button
         var pt:Point = new Point(event.stageX, event.stageY);
-        var pt2:Point = globalToLocal(pt);
+        var pt2:Point = track.globalToLocal(pt);
         pt = thumb.globalToLocal(pt);
         _clickOffset = pt;
     }

    //---------------------------------
    
    /**
     *  Handle mouse-down events on the scroll thumb. Records the difference
     *  between positions.
     */
    protected function thumb_mouseDownHandler(event:MouseEvent):void
    {

    private var _thumbSize:Number = 0;
    
    /**
     *  The size of the thumb on the logical track in the 
     *  units of the subclass, which must be consistent with 
     *  trackSize, pointToPosition and valueToPosition. The 
     *  default thumbSize on the logical track is 0.
     * 
     *  @default 0
     */
