The PureMVC Framework Code at the Speed of Thought

first i load a module , then i unload it ,
when i load it again , module's ApplicationFacade return a null instance.

i trace it in code, find that instanceMap[ key ] is not null,but cast it return null.

who can help me?

        public static function getInstance( key:String ) : ApplicationFacade
        {
        trace(key);
        trace("instanceMap[ key ]:");
        trace(( instanceMap[ key ] == null )?"nothing":instanceMap[ key ]);
       
            if ( instanceMap[ key ] == null ) instanceMap[ key ]  = new ApplicationFacade( key );
        trace("instanceMap[ key ]:");
        trace(( instanceMap[ key ] == null )?"nothing":instanceMap[ key ]);
        trace(instanceMap[ key ] as ApplicationFacade);
            return instanceMap[ key ] as ApplicationFacade;
        }

               
 moduleLoader.applicationDomain = ApplicationDomain.currentDomain;