 
     /**
      *  @private
+     *  SDT - Scrollbar Display Threshold.  If the content size exceeds the
+     *  viewport's size by SDT, then we show a scrollbar.  For example, if the 
+     *  contentWidth >= viewport width + SDT, show the vertical scrollbar.
+     */
+    private static const SDT = 1.0;
+
+    /**
+     *  @private
      *  Used by updateDisplayList() to prevent looping.
      */
     private var invalidationCount:int = 0;

        var viewportH:Number = isNaN(explicitViewportH) ? (h - (minViewportInset * 2)) : explicitViewportH;
                        
        // Decide which scrollbars will be visible based on the viewport's content size
        // and the scroller's scroll policies.
        
        var oldShowHSB:Boolean = hsbVisible;
        var oldShowVSB:Boolean = vsbVisible;

                if (vsb && viewport)
                { 
                    vAuto = true;
                    vsbVisible = (contentH >= (viewportH + SDT));
                }                        
                break;

