Preview showing two cameras alpha'd over each other?

When I press play in Unity I get this. Exporting seems to work fine, but I'm seeing worse performance than I'd expect, so I don't know if it's still rendering both cameras but only showing one.

That image is a bit confusing, but what's happening is there are two cameras overlaid over each other. I've got my OVRCameraRig scripted to follow a "wingsuit" gameobject, and the gameobject reacts to the hmd's orientation. Both cameras react when I move the HMD around, as if there are two wingsuits, or two OVRCameraRigs attached to the one wingsuit. There's definitely only one of each, and if I disable the OVRCameraRig, nothing at all comes up on the preview.

Any ideas?

Edit: It only seems to happen after I've built the project for the first time since loading Unity up.