For at least one big dataset (WholeBody.pic.gz), GPU-based volume rendering is not functioning properly. GPU-slicing yields no volume rendering at all, and the GPU-raycasters being extremely slow. In one case, the following errors were put out:

"
701.33 ext.rnd.gpuVolMap3d: initializing gpu-raycast-vr (vtkOpenGLGPUVolumeRayCastMapper)
after uniforms for textures ERROR (x501) Invalid value
framebuffer has an attachment error
framebuffer has an attachment error
SetupRender ERROR (x506) invalid framebuffer operation ext
framebuffer has an attachment error
framebuffer has an attachment error
render clipped block 1 ERROR (x506) invalid framebuffer operation ext
render clipped block 1 ERROR (x506) invalid framebuffer operation ext
"

And on closing:

"
701.33 ext.rnd.gpuVolMap3d: initializing gpu-raycast-vr (vtkOpenGLGPUVolumeRayCastMapper)
after uniforms for textures ERROR (x501) Invalid value
framebuffer has an attachment error
framebuffer has an attachment error
SetupRender ERROR (x506) invalid framebuffer operation ext
framebuffer has an attachment error
framebuffer has an attachment error
render clipped block 1 ERROR (x506) invalid framebuffer operation ext
render clipped block 1 ERROR (x506) invalid framebuffer operation ext
"

These messages have not been reproducible so far although the rendering issue still remains.