UIScrollBarSkinning

Hi all

i am trying to skin UIScrollBar using action Script (RectBorder class). the up arrow, down arrow n scroll track are workin fine. but the scrollThumb is going haywire. it is rendering as its supposed to but its not behaving as it should be. i have added the code for
ScrollThumbTopUp (all subcomponent code is similar except for class name and skin registration portion).


import mx.skins.RectBorder;
import mx.core.ext.UIObjectExtensions;
class ScrollThumbTopUp extends RectBorder
{
    static var symbolName:String = "ScrollThumbTopUp";
    static var symbolOwner:Object = ScrollThumbTopUp;
    
    function size():Void
    {
        var c:Number; // color
        var borderStyle:String = getStyle("borderStyle");
  trace("topUp");
  c = 0x000000;
        clear();
        beginFill(c, 100);
        drawRect(4, 0,10 ,4);
        endFill();
    }
    
    // Required for skins.
    static function classConstruct():Boolean
    {
        UIObjectExtensions.Extensions();
        _global.skinRegistry["ScrollThumbTopUp"] = true;
        return true;
    }
    static var classConstructed:Boolean = classConstruct();
    static var UIObjectExtensionsDependency = UIObjectExtensions;
}