add video with "entity/polygon", the video flip horizontal

var viewer = new Cesium.Viewer('cesiumContainer', {
    showRenderLoopErrors : false,
    shouldAnimate : true

var videoElement = document.getElementById('trailer');

var entity = viewer.entities.add({
        polygon: {
            hierarchy: Cesium.Cartesian3.fromDegreesArrayHeights(110,30,10000, 110,40,10000, 120,40,10000, 120,30,10000),
            height: 10000,
            material: videoElement,
            perPositionHeight: true,
    I want to use "entities" add video with "polygon", when I set the parameter "perPositionHeight" true, the video is normal,
    but when I set the parameter "perPositionHeight" false, the video is flip horizontal, how to solve the problem? Thank you.

Thanks for reporting this. I think this is a bug. I opened a GitHub issue for it, so we’ll see if anyone has any solutions: