How to fix the problem that label be covered by billboard

Here is the code in sandcastle

See this modified example Sandcastle

label: {
text: “Label on top of scaling billboard”,
font: “20px sans-serif”,
eyeOffset : new Cesium.Cartesian3(0, 0, -1000)
//disableDepthTestDistance: Number.POSITIVE_INFINITY,

Thanks for the reply.
most time we need use terrain in our system.
so this is what exactlly happening.