Steps to reproduce:
1. Open the attached project
2. Open the scene.unity
3. Play the scene
4. See the output in console:
Before set@Start --->1
Before set@Start --->20
After Override@Start --->20
After Override AnimationClip@Start --->0 (this should be 20)

Actual result: StateMachine was reseted
Expected result: Overriding a clip in an override controller should not reset the StateMachine

Reproduced with: 5.5.4p2, 5.6.0a1
Not reproduced with: 5.6.0a2, 5.6.2p4, 2017.1.0p1, 2017.2.0b4, 2017.3.0a1