I am using Entity Framework and Caliburn.Micro to implement an MVVM application.
Basically, I have set up AuthorModel and BookModel in a one to many relationship - a
As Eben mentions, the Author referenced by the ItemsSource will be a different object (although it happens to reference the same entity).
I think your approach of using a new DbContext for both of your windows is correct, you can run into problems if you have persisting/shared DbContexts; it makes sense to load an EditWindow with a new context, perform your edits, and dispose of the context.
One option is to Detach your Book entity from the old DbContext, and Attach it to your new context: (a good explanation here Entity Framework 4 - AddObject vs Attach).
I would probably just favour using the passed Book entity to reload the selected Book from the new context e.g. using DbSetSelectedItem (rather than the one you're passing across windows).