Flex Module issue with Panel

Question

Hello everyone. I have the following problem.
In my application I have several modules and each of them have components CollapsableTitleWindow (extends Panel). After opening the window it is added to the container which is in the main application (CollapsableTitleWindowContainer). In these windows you can open another window (and so on).
Now, what is the problem. When I change (reload) any module and I want to open a new window (sub window) with the already loaded window I get this error:
TypeError: Error #1009: Cannot access a property or method of a null object reference.
at mx.containers::Panel/layoutChrome()[C:\autobuild\3.2.0\frameworks\projects\framework\src\mx\containers\Panel.as:1405]
at com::CollapsableTitleWindow/layoutChrome()[D:\Flex 3 Workspace\WesobCrm\src\com\CollapsableTitleWindow.as:216]
at mx.core::Container/updateDisplayList()[C:\autobuild\3.2.0\frameworks\projects\framework\src\mx\core\Container.as:2867] (...)
Indicates that the main applications have object Panel
Please help.
P.S. I found a similar problem on http://www.nabble.com/Flex-Module-issue-with-Panel-td20168053.html
ADDED: I extendes the Panel class and do something like that:
override protected function layoutChrome(unscaledWidth:Number, unscaledHeight:Number):void
                use namespace mx_internal;
                if(!(mx_internal::titleBarBackground is TitleBackground)) {
                        mx_internal::titleBarBackground = new TitleBackground();
                super.layoutChrome(unscaledWidth, unscaledHeight);                     
But now i had something like that: Before After
You can see that it loos style declaration.H

Answer 1

Thanks for the anserw.
I don't exacly understand all but i found a solution for my problem and it works.
Could you tell me if this is ok ?
I Add in my main app
public function getProductWindow():ProductWindow {
    return new ProductWindow();
And in the module i change
From var productWindow:ProductWindow = new ProductWindow();
To var productWindow:ProductWindow = Application.application.getProductWindow();