How to reproduce:
1. Open the "case_1263707.zip" project and open SampleScene
2. Select the TimelineObject in the Hierarchy window
3. Enter the Play mode
4. Observe the Timeline window, the Timeline duration Marker is moving
5. Pause the game
// If using Timeline 1.2.6 - 1.3.5
6. Select DirectionalLight (or any other Game Object in the Hierarchy window)
7. Select TimelineObject in the Hierarchy window
8. Unpause the game
9. Observe the Timeline window, the Timeline duration Marker is not moving
// If using Timeline 1.4.0 - 1.5.0-preview.4
6. Unpause the game
7. Observe the Timeline window, the Timeline duration Marker is not moving

Expected result: Timeline duration Marker is moving after unpausing the game
Actual result: Timeline duration Marker is not moving after unpausing the game

Reproducible with: 2019.4.8f1, 2020.1.2f1, 2020.2.0a20
Not reproducible with: 2018.4.26f (Timeline part of the Editor, no bug)
Package versions tested: 1.2.6 - 1.3.5 (repro steps #1), 1.4.0 - 1.5.0-preview.4 (repro steps #2)