How to reproduce:
1. Make a project with the user's attached 'timeline_issue.unitypackage', open 'timeline_issue' scene
2. Enter Play mode, make sure that 'Player' has an Animation playing
3. Select 'mesh_prefab' under Player -> Visual and observe that the local position can be modified
4. Select 'TimelineDirector' and double-click on the playable to open up the Timeline window
5. Press Play on the Timeline window and let the Animation finish
6. Repeat Step 3

Expected results: 'mesh_prefab' local position is changed
Actual results: 'mesh_prefab' local position doesn't change, appears to be locked

Reproducible with: 2019.1.8f1, 2019.2.0b8, 2019.3.0a7
Could not test with the earliest 2019.1 version and before that due to Playable corruption.