<!-- Thanks for helping us improve Cesium! Please describe what the expected behavior is vs what actually happens. Creating a Sandcastle example (https://cesiumjs.org/Cesium/Build/Apps/Sandcastle/) that reproduces the issue helps us a lot in tracking down bugs. Paste the link you get from the "Share" button in Sandcastle below. --> Sandcastle example: [link](http://localhost:8080/Apps/Sandcastle/index.html#c=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) Browser: Firefox Operating System: Linux <!-- If you can also contribute a fix, we'd absolutely appreciate it! Fixing a bug in Cesium often means fixing a bug for thousands of applications and millions of end users. Check out the contributor guide to get started: https://github.com/CesiumGS/cesium/blob/master/CONTRIBUTING.md Just let us know you're working on it and we'd be happy to provide advice and feedback. --> Found by @lilleyse in #9399.  
