Reproduction steps:
1. Open the attached project "ExampleProject.zip"
2. In the Project window, double click the Asset "TimelineExample.playable"
3. In the Timeline window select "Track Asset Example"
4. In the Inspector change the value of the "Example" variable to "LocalizedStringTable_Example"
5. Deselect "Track Asset Example"
6. Select "Track Asset Example" again
7. Observe the value of "Example" in the Inspector window

Expected result: The value is saved as "LocalizedStringTable_Example"
Actual result: The value is reverted to "None"

Reproducible with: Timeline 1.2.18 (2019.4.38f1), 1.4.8 (2020.3.33f1), 1.6.4 (2021.3.0f1), 1.7.1 (2019.4.38f1, 2020.3.33f1, 2021.3.0f1, 2022.1.0b16, 2022.2.0a10)

Notes:
- Does not reproduce with variable types such as int, string, GameObject, ScriptableObject
- Does not reproduce when assigning a LocalizedStringTable to a MonoBehaviour, or a ScriptableObject