             {
                 var hspDelta:Number = vp.getHorizontalScrollPositionDelta(navigationUnit);
                 if (!isNaN(hspDelta))
+                {
                     vp.horizontalScrollPosition += hspDelta;
+                    if (vp is IInvalidating)
+                        IInvalidating(vp).validateNow();
+                }
             }
             event.preventDefault();
         }            

import spark.components.supportClasses.SkinnableComponent;
import spark.core.IViewport;
import spark.core.NavigationUnit;
import mx.core.IVisualElement;
import mx.core.IVisualElementContainer;
import mx.core.LayoutDirection;

            {
                var vspDelta:Number = vp.getVerticalScrollPositionDelta(navigationUnit);
                if (!isNaN(vspDelta))
                {
                    vp.verticalScrollPosition += vspDelta;
                    if (vp is IInvalidating)
                        IInvalidating(vp).validateNow();
                }
            }
            event.preventDefault();
        }
