When you change tabs between documents of the same type in the same tab group events such as LastActiveDocumentChanged are not fired...this can be quickly reproduced using the MvvmDocumentWindows example. in MainView.xaml add an event for LastActiveDocumentChanged to the docking:DockSite. Run the application and add a second document.When switching between Document1 and Document2 the event is not fired however if you switch between the WelcomeDocument and Document1 it is. If you move Document2 to a new tab group, then switching between documents the event is fired correctly. This same error applies to all events such as WindowActivated/WindowDeactivated etc.