VTK_GROUP_ENABLE_Rendering doesn't enable RenderingVolumeOpenGL2

On a clean build of VTK the RenderingVolumeOpenGL2 is not enabled even though RenderingOpenGL2 and RenderingVolume are.

 make help | grep Rendering
... RenderingCore-hierarchy
... RenderingCore
... RenderingFreeType
... RenderingFreeType-hierarchy
... RenderingContext2D-hierarchy
... RenderingContext2D
... RenderingAnnotation-hierarchy
... RenderingAnnotation
... RenderingVolume-hierarchy
... RenderingVolume
... RenderingLabel
... RenderingLabel-hierarchy
... TestingRendering-hierarchy
... TestingRendering
... RenderingLOD
... RenderingLOD-hierarchy
... RenderingImage-hierarchy
... RenderingImage
... RenderingOpenGL2
... RenderingOpenGL2-hierarchy
... RenderingGL2PSOpenGL2
... RenderingGL2PSOpenGL2-hierarchy
... vtkRenderingLabelCxxTests
... vtkRenderingLODCxxTests
... vtkRenderingImageCxxTests
... vtkRenderingGL2PSOpenGL2CxxTests
... vtkRenderingAnnotationCxxTests
... vtkRenderingOpenGL2CxxTests
... vtkRenderingCoreCxxTests