You can see in your video, even in 4.1 the bone compensation doesn't work. If it did, the hair bones would not move. Bone compensation can't be done in certain circumstances, such as when any constraint is applied with 100% mix or when a transform, path, or IK constraint has > 0% translate mix. This affects bone the bones being moved and the child bones being compensated.
In 4.1 attachment compensation is applied, so the head mesh attachment doesn't move, even though the bones do. This works well for translation in the example you showed, but it doesn't work for rotation, scale, or shear. There are also other cases where it doesn't work well. Try it on the gun bone (in 4.1) and you'll see the gun region attachment moves incorrectly.
In 4.2 we don't apply attachment compensation in those circumstances because it often can't work correctly. You can temporarily set the constraint mixes to zero, use compensation, then set them back.
