Strange behavior of vtkVolume + transparent vtkPolyData

OS: Windows 10 Pro VTK version: 9.0.1 GPU: Nvidia Quadro K2200

Hello everyone.

I'm currently facing the problem already addressed within the VTK Mailing List in 2015 - see here

It was mentioned, that there is indeed a proplem with transparent polyData rendered besides a volume. As soon as the polyData gets an opacity below 1.0 it appears to be completely behind the volume. The user in the mailing post mentioned that this issue will be addressed in VTK 8.

There was no response since then. Are there any updates right now, which enable the rendering of transparent polydata within a volume?

In my case, I'm using the vtkSmartVolumeMapper and a cube polyData object (cubeSource, polyDataMapper, actor) with an opacity of 0.8.