High CPU usage with static 3D scene

CPU load has a strange behavior.
When running the attached test, CPU usage goes up at the beginning when object in the scene are moving. When object in the scene stops moving then the CPU load goes even higher, while I was expecting that since rendering is not needed it would go down (See attached CPU plots).
Also reducing number of 3D obects (500 spheres) It is possible to see that CPU usage do not decrease after stopping motion, even if it does not go up.

Setting renderPolicy to onDemand does not change the results.