Silverlight DataForm: When is the Dirty flag coming up?

I'm using Silverlight 3 with RIA Services without DomainDataSource.

When binding to a PagedCollectionView (or ObservableCollection) in a MVVM the Dirty State on the Dataform doesn't come up (the asteriks). When I change an assocation chosen via a childview the Dirty flag comes up after changing an assocation twice. (I change the assocation in code.)

I suspected the Dirty f开发者_如何学Golag comes up with the implementation of INotifyPropertyChanged, which ofcourse all entities are implementing correct, but clearly it isn't.

When does the Dirty flag comes up?

Thank you for your answer. I worked around the problem I had. But you are right about the IEditableObject. When the dataforms commits, the entity is Dirty and the asteriks is visible.