Billboard ordering incorrect when using disableDepthTestDistance

[hpinkos]

When the disableDepthTestDistance is greater than the distance from the camera to the billboard, the wrong billboard renders on top. In this example, the blue billboard has a greater height than the red billboard so it should be visible. However, the red billboard is instead.

var viewer = new Cesium.Viewer('cesiumContainer');
var scene = viewer.scene;
var camera = scene.camera;
var billboards = scene.primitives.add(new Cesium.BillboardCollection());
billboards.add({
    image : '../images/Cesium_Logo_overlay.png',
    color: Cesium.Color.RED,
    position : Cesium.Cartesian3.fromDegrees(0, 0),
    disableDepthTestDistance: Number.POSITIVE_INFINITY
});

billboards.add({
    image : '../images/Cesium_Logo_overlay.png',
    color: Cesium.Color.BLUE,
    position : Cesium.Cartesian3.fromDegrees(0, 0, 100),
    disableDepthTestDistance: Number.POSITIVE_INFINITY
});

camera.position = Cesium.Cartesian3.fromDegrees(0, 0, 4000);
camera.direction = Cesium.Cartesian3.negate(Cesium.Cartesian3.UNIT_X, new Cesium.Cartesian3());
camera.up = Cesium.Cartesian3.clone(Cesium.Cartesian3.UNIT_Z);