The image material of a polygon with height distorted

I have created two entity with same image material.
one is polygon with height showing administrative division.
the other one is rectangle without height showing the bbox of polygon.
The picture has been distorted between them.

the gif above shows this things:
when i click the “show” button, the entity with height of 5 will show with a blue outline.
when i click the “hide” button.the entity will hide.
below the entity of polygon is a rectangleGraphics with the same image material.
my question is why the image distorted
//below is polygon
polygon: {
hierarchy: Cesium.Cartesian3.fromDegreesArrayHeights(arrPos),
material: imgTop,//this is a img url
height: heightExtruded,//this value is 5
outline: true,
outlineColor: Cesium.Color.BLUE,
outlineWidth: 20.0,
//below is rectangle
rectangle: {
coordinates: Cesium.Rectangle.fromDegrees(west, south, east, north),//the bbox of the polygon
outline: true,
outlineColor: Cesium.Color.YELLOW,
outlineWidth: 20,
material: imgTop,//the same image url with the polygon