Bone chanches it's roll even in Rest Pose

Question

I'm doing a rig and faced with the following problem. The bone and it's parent have no any constraints or driver, but the bone changes it's roll even in Rest Pose. I see that at first time.

Here is a screenshoot:

And file: https://drive.google.com/file/d/1WMr0iYCVd6Oq_r9mt8lo9fNM8D6hz3x3/view?usp=sharing

Any idea what's going on?

Answer 1

It's just a display tolerance, probably due to the extra tiny dimensions of the bone, if you tie a mesh to the bone, you wil see that there is no shift, even when the bone display is shifting from edit to pose mode.