How to reproduce:
1. Open the attached project
2. Open the test.unity scene
3. From the Project window drag "Cube" prefab to the scene window
4. Go to the Inspector window -> Transform -> Position and change Y value to 777 then save the scene
5. Go to the Menu bar -> ReplacePrefab and select Test then save the scene
6. Close the project and open it again
7. Move GameObject Cube in the Scene view

Expected: Camera doesn't follow any game objects
Actual: Camera gets locked on a GameObject

Reproducible with: 5.6.6f2, 2017.2.0a3, 2017.2.5f1, 2017.3.2f1, 2017.4.17f1
Not reproducible with: 2018.1.9f2, 2018.2.19f1, 2018.3.0f1, 2019.1.0a11