How to reproduce:
1. Open the "1235781 repro" project
2. Open the "TestScene" Asset from the Assets folder
3. Create a new Timeline and a new Animation Asset
4. Create a new empty GameObject in the Scene
5. Attach a Playable Director, Animator and Audio Source to the GameObject
6. Assign the created Timeline Asset to the Playable Director
7. Open the Timeline assigned to the Playable Director in the previous step
8. Create an Animation and an Audio track on the Timeline
9. Bind the GameObject to the output of both of the Tracks
10. Put the created Animation Asset anywhere on Animation Track
11. Put the "smb_coin.wav" from the Assets folder anywhere on the Audio Track
12. Turn off the Timeline Preview
13. Drag the GameObject into the Assets folder to save it as a Prefab
14. Select the newly created Prefab
15. Open the Timeline assigned to the Playable Director of the Prefab

Expected result: there are no warnings since the Animation Track and the Audio tracks are referencing an instance of the Prefab
Actual result: the editor throws warnings about the Prefab asset being assigned to the output of type Animation

Reproducible with: 2018.2.0a5, 2018.2.21f1, 2018.4.21f1, 2019.3.10f1 (1.2.14), 2020.1.0b5 (1.3.2), 2020.2.0a7(1.4.0-preview.3)
Not reproducible with: 2017.4.39f1, 2018.2.0a4

Notes:
-This Prefab is set up correctly and Sound will be heard if the game is played
-If the "TestObject" from the "SampleScene" Scene is selected and its corresponding Timeline is viewed, by clicking an object bound to a Track you can see that the instanced version of the Prefab and not the main Prefab is bound to the output of the Track. This is shown in the "ObjectInTheScene.mp4" video