Finding the local camera.position in an XR session

I’m having trouble getting the correct camera,position, as the behaviour of that variable seems to change when we enter an XR session with a render loop.

I have a group, and I add an object to it. When I move the group, the local position of the object stays at 0,0,0. However, when that object is a camera, then the position seems to change after awhile unexpectedly as show in the code below. If this is happening, how can I find the actual local position of the camera?

Here’s my code, below is the output I expected, and the output I actually get:

import * as THREE from ‘three’;
import { VRButton } from ‘./three/examples/jsm/webxr/VRButton’;

var scene = new THREE.Scene();
var camera = new THREE.PerspectiveCamera();
var renderer = new THREE.WebGLRenderer();
renderer.xr.enabled = true;
renderer.xr.setReferenceSpaceType(‘local’);
document.body.appendChild(renderer.domElement);
document.body.appendChild(VRButton.createButton(renderer));

renderer.xr.addEventListener( ‘sessionstart’, function(){
var group = new THREE.Group();
var object = new THREE.Group();

scene.add(group);
group.add(object);
group.add(camera);

var vector = new THREE.Vector3();

log_positions();
group.position.z--;
log_positions();
setTimeout(
    log_positions,
    50, // after about 10ms, the problem occurs
);

renderer.setAnimationLoop(function(){
    renderer.render(scene, camera);
});

function log_positions() {
    console.log("object.position: " + object.position.x + ", " + object.position.y + ", " + object.position.z);
    console.log("camera.position: " + camera.position.x + ", " + camera.position.y + ", " + camera.position.z);
}

});

What I expected to see was:
object.position: 0, 0, 0
camera.position: 0, 0, 0
object.position: 0, 0, 0
camera.position: 0, 0, 0
object.position: 0, 0, 0
camera.position: 0, 0, 0

But what I actually see is:
object.position: 0, 0, 0
camera.position: 0, 0, 0
object.position: 0, 0, 0
camera.position: 0, 0, 0
object.position: 0, 0, 0
camera.position: 0, 0, -1 <----- ???

Thank you!