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?

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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.