There is yet another bug in Studio 18.6.
When a 3D Blu-ray disc has been authored, the resultant disc cannot be played in 3D. The 3D blu-ray player fails to recognise the disc as being in 3D and consequently only plays it in 2D. I have managed to verify that the video file itself is indeed a full 3D image. The disc seems to be lacking whatever flag is required to be on it to signal to a player that it is a 3D disc. This is true for both side-by-side 3D and for Multistream 3D.
Playing the disc on a PC based player such as PowerDVD works, but PowerDVD plays the stream file based on its content and not what the disc claims to contain.