[flexcomponents] Custom component in design time, question

[lytvynyuk]

I have an issue to let my component look same in runtime and design
time.

Component is container which looks like that:

     public class MyContainer extends Canvas
     {
        componentsEnvelop:LayoutContainer = new LayoutContainer();

        override public function initialize():void {
             componentsEnvelop.percentHeight=100;
             componentsEnvelop.percentWidth=100;
             componentsEnvelop.setStyle("backgroundColor","#ffffff");
             super.initialize();
        }

         override public function
addChild(child:DisplayObject):DisplayObject {
             return componentsEnvelop.addChild(child);
         }

         private function
addChildSpecial(child:DisplayObject):DisplayObject {
             return super.addChild(child);
         }

         override public function
removeChild(child:DisplayObject):DisplayObject {
             return componentsEnvelop.removeChild(child);
         }

         private function doLayout():void {
             this.addChildSpecial(componentsEnvelop);
             this.addChildSpecial(titleBar);
             titleBar.addChild(_label);
         }

         override protected function createChildren():void
         {
             super.createChildren();
             doLayout();
         }
     }

in run time everything looks ok, but in design time in Flex Builder all
component I put inside my MyContainer displayed always beyond the
LayoutContainer and therefore invisible. How to handle that cituation,
what method should be override to intercept child add in design time?