Tree Creator trees

Repro Steps:
1. Create new project
2. Create a Tree object via GameObject -> 3D Object -> Tree
3. Create a Terrain object via GameObject -> 3D Object -> Terrain
4. Select the Terrain
5. Go to the Paint Trees tab of the Terrain
6. Click Edit Trees then Add Tree
7. Open the object selector for the object field in the Add Tree popup
8. Select the asset for the Tree you created
9. Click Add
10. Popup window should close. Now select the Tree in the Terrain Inspector
11. Paint some instances on the Terrain
12. Select the Prefab Instance of the Tree from the Hierarchy
13. Change the scale of the Prefab Instance using the Inspector or the transform gizmos
14. Undo
15. Should see painted TreeInstances change in scale
16. Select the Tree asset in the Project Window and you will see that the scale change was applied to the prefab

Expected Result: the scale change for the prefab instance is not applied to the scale for the prefab source when undoing
Actual Result: the scale change for the prefab instance is applied to the prefab source scale when undoing