OVRSceneManager loses its transforms when additively loading scenes

Found this bug - if you are additively loading scenes and you have the OVRSceneManager in your hub scene (which you need to) - and there is a scene additively loaded from the start which you've set to the Active scene - then OVRSceneManager will place its wall,ceiling etc anchor objects that it creates in that scene - and then when you unload that scene - they'll be lost - and OVRSceneManager won't know there's a problem but if you try to access the Ceiling's transform for example it'll throw up a null reference.
I fixed this in OVRSceneManager by moving the prefabs etc that it spawns to be its children in the hierarchy.