Following 7451dd2d (vtkDisplaySizedImplicitPlaneWidget/Representation: Implementation) and cd42f785 (vtkCoordinateFrameWidget: Implementation), the class called vtkInteractionCallback was defined multiple times in the following classes:
This violates the one definition rule (ODR) and can lead to undefined behavior.
The issue "started" back in 2012 with commit dd214570 (ENH: Automatic plan
orientation in vtkImplicitPlaneWidget2) added the class
that was using a generic name.
Then, in 2015, following effa1ddd (Added new widget: vtkImplicitCylinderWidget), the pattern
of using the generic classname
vtkInteractionCallback has been copied into
introducing a first occurrence undefined behavior later addressed in e8170ff5 (Fix multiple definitions