the new mitk::GPUVolumeMapper3D is located in mitkCoreExt,
and becomes registered by the CoreExtFactory for mitk::Images,

however on some MITK builds, the new mapper isnt registered,
and the old VolumeVtkMapper3D from the core is used.

i am investigating that problem,
but one working solution will be to replace the core mapper with the new mapper from coreext.