How to reproduce:
1) Create 2 GameObjects
2) Attach a Tracked Pose Driver to each GameObject
3) Change the pose source for one of the Tracked Pose Driver
4) Select both gameobjects

Expected:
The Tracked Pose Drivers retain their original values unless specifically edited by the user.

Observed:
Both Tracked Pose Driver pose sources are set to the value of the pose source of the Tracked Pose Driver that was selected first.

Observed in trunk 3e681eca9b01 (build 16 July 2018)
Reproduced in 2017.2.0f1. Tracked Pose Driver does not seem to exist in 2017.1 (checked 2017.1.0f3)