Diagram Shapes' property is bound to property from the ViewModel.
Case 1) Using GraphSource =>Shapes DataContext is automatically apllied. GraphSource is set to null or changed.
Or
Case 2) Not using Graphsource. Shape's DataContext is set manually (in code behind). Diagram.Clear() is invoked.

Result: Binding Expression erors in Output indicate missing properties - these are bound properties of the shapes.