Problems extending NSPersistentDocument Core Data Tutorial

FROM : Simon
DATE : Sun Nov 18 21:42:30 2007

Hi

I want to extend the core-data application from the 
NSPersistentDocument core data tutorial with some additional 
functionality. I've added a sheet to manage a tree of departements. 
The Department entity has two additional relationships, a parent and 
an inverse children relationship. I've successfully managed to bind an 
NSTreeController and an NSOutlineView. Now, I want to add an 
NSPopupButton to the new object sheet which allows to choose the 
department for a new employee.

However, if I launch the application and add some departments and then 
try to add a new employee, the NSPopupButton is not updated (that is, 
it stays empty). If I save the document, reopen it and add a new 
employee, the popup button is properly populated. Below the changes 
I've made in the new Employee Sheet NIB.

* NSArrayController for the departements
** managedObjectContext bound to managedObjectContext of File's Owner
* NSPopupButton for the departements
** Content bound to array controller arrangedObjects
** Content Values bound to array controller arrangedObjects key path 
name
** Selected Object bound to Object Controller arrangedObjects key path 
department

If I bind the array controller's managedObjectContext to the 
documentManagedObjectContext of File's Owner, the popup menu is 
populated (I can't complete the sheet because the department is from a 
different managed object context and that is obviously not allowed). 
How can I make sure that the changes from the departments sheet are 
visible in the new object sheet's popup button?

Thanks
Simon