QmitkNodeDescriptorManager is a CoreUI class.
QmitkNodeDescriptorManager::Initialize() adds NodeDescriptors for PlanarFigure classes, but PlanarFigures are part of MitkExt. NodeDescriptors should therefore be added in MitkExt or QmitkExt or a QmitkExtActivator class in a QmitkExt bundle, if that exists (analogous to DiffusionImaging).
This is nothing serious, but it will help to keep the Core clean.
Can be done by anyone at a bug squashing party.