So you have disabled zoom levels in MP to get 3D activated automatically ? Is it working all the time without enabling it again after playing a 2D file?
I tested again and it's more that way: The TV runs in 4k. If i start a 3D film it switches to 1080p and i see only a quarter of picture, but in fullscreen. If I push the blue Button (zoom switching, Media Center Remote) the zoom is set to source and i see the whole picture, parallel TV recognize 3D in switch in 3D mode. I hope I have tomorrow a bit more time, so i will post a log and some screenshots.