message: 50% of bugs are caused by missing clone().
  In this case, TFS#927608: rendering clip mask texture leaves depth test
  off for subsequent rendering.
diff: @@ -308,7 +308,7 @@ export class ClipMaskVolume implements RenderClipVolume {
  // Render clip geometry as a mask
  System.instance.frameBufferStack.execute(this._fbo, true, () => {
  - const prevState = System.instance.currentRenderState;
  + const prevState = System.instance.currentRenderState.clone();
  const target = exec.target;
  System.instance.applyRenderState(state);
  