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

        // Scroll event.delta "steps".  If the VSB is up, scroll vertically,
        // if -only- the HSB is up then scroll horizontally.
         
        if (verticalScrollBar && verticalScrollBar.visible)
        {
            navigationUnit = (event.delta < 0) ? NavigationUnit.DOWN : NavigationUnit.UP;

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