Relate to NavigationBar expand/minimize behaviour

My application has interface looks like Microsoft Outlook 2007, except I use a ribbon instead of menu toolbar on top of the window. I used CommandBindings for the list contained inside the app menu button.
When I select a NavigationPane in NavigationBar on left side of the window, I could access the app menu button and see the list contained inside app menu button has enabled items as expected. (means that CommandBindings is working in this case). But, when I minimize or expand the NavigationBar, and I try to access the app menu button, the list contained inside app menu button has all grayed out items eventhough the selected NavigationPane still in highlighted mode. If I reselect the highlighted NavigationPane when the NavigationBar still in expanded/minimized mode, the list contained in app menu button has enabled items again. This issue could reproduce easily.