As far as I can see the UI-elements connected to "Scaling" are not used anywhere in MITK. The only class that uses the ui-file is the QmitkRegistrationManipulationWidget. Here only the "Translation" and "Rotation" elements are connected and used. If this is desired we should remove the elements for "Scaling". The group for the UI elements is even explicitly set to this->groupScale->setVisible(false); inside QmitkRegistrationManipulationWidget.