Physics constraint angular motor does not preserve angular momentum

Hi. I noticed that physics constraint angular motors does not preserve angular momentum of two bodies system when i set target motor rotation to complex angle, for example 30yaw, 45 pitch. When im change target rotation only one axis, angular momentum of bodies system is saving. In real life, without any external forces angular momentum of system cannot be changed.

Example video link - 2021 03 09 16 03 10 - YouTube

Download project files link - momentum.7z - Google Drive

How solve this problem? This is bug?

2 years later and I’m encountering this problem too… Anyone found a solution to this?