SceneKit - allowsCameraControl plus programmatic camera control?

Question

I have a scene with an explicit camera in it, and with allowsCameraControl enabled. Before the user modifies the camera, I can programmatically set aspects of the camera and camera node. For example fieldOfView, position. But once the user interacts with the camera, eg pan or rotate, those fields no longer have any effect. I've walked through the scene and verified that there's still only a single camera, and I'm verifying that the values I'm applying programmatically are not being stomped by something. It's as if, once the user started interaction, a copy of my camera node was made, and that's now the active camera. However a recursive search from the root reveals only one camera.