targeting Smart bone disable Targeting other bones in action

[Hamedss]

Hi.
Build this simple rig:
1. Create 4 Bones A - B - C - D . these are free and not parented to other bones. Bone A directed to up.
Put them in places so B is above A and D is Above C
2. Set D as target of C
3. Build smart action with A that rotating to right make D move to right.
4 . If you check the action it works

If you set B as target of A and move B the action works But C not targeting the D and Just moves to right.
Why if smart bone target to another bone the bones in action lost their target?
Link to rig
https://file.io/qHbB9yEMoT0Q