this drove everythign crazy.

And now it's fine. Apparently setting something to false still makes it
true...

src/Cameras/babylon.camera.ts

@@ -623,7 +623,6 @@
 
                         //Right eye
                         this._rigCameras[1].viewport = new Viewport(0.5, 0, 0.5, 1.0);
-                        this._rigCameras[0].setCameraRigParameter("left", false);
                         this._rigCameras[1].setCameraRigParameter('eyeParameters', rightEye);
                         this._rigCameras[1].setCameraRigParameter("frameData", rigParams.frameData);
                         this._rigCameras[1].setCameraRigParameter("parentCamera", rigParams.parentCamera);