I think this is a bug in Catel 2.4 - Calling Close() on a ViewModel that is decorated with an IsInterestedAttribute doesn't seem to unsubscribe from change notifications on the "interested in" viewmodel type.
Looking at the source code, ViewModelBaseWithoutServices.Close() calls UnregisterCommands() but doesn't do anything to remove the InterestedInAttribute.
In fact, I see in ViewModelManager that there is a method, RemoveInterestedViewModelInstance whose summary states,
"...The <see cref="IViewModel"/> class will automatically unregister itself from the manager by using this method when decorated with the <see cref="InterestedInAttribute"/>."
However, right-clicking this method and choosing "Call Hierarchy" shows that all calls to this method are from ViewModelManagerTest.
Am I wrong in thinking that the Close() method should call ViewModelManager.RemoveInterestedViewModelInstance?