ARFoundation 3: ARCameraBackground custom material not working

Trying to use a custom material to draw the camera background, but it doesn't appear to have any effect. I even tried using a material that returns only red fragments, but the video feed still looks the same as ever.

Using ARFoundation 3.0.0.preview-2

 

Ok so this seems to be because ARCameraBackground can't have its useCustomMaterial property changed after it starts up. I tried a solution where I destroy the ARCameraBackground component and add a new one to the game object and either add a custom material or remove it, but it seems like the first one doesn't clean up after itself because the background is only black :/

I'd assume it has something to do with how the CommandBuffers are set up...