How to reproduce:
1. Open the attached "1293801_Repro" project
2. Open the Scene "SampleScene"
3. In the Hierarchy select the "GameObject"
4. In the Inspector under the TetMeshPro - Text Component change Font Style

Expected results: A blue line appears next to the property name and the property name gets bolded identifying that it was modified
Actual results: No blue line appears next to the property name and the property name doesn't get bolded identifying that it was modified

Reproducible with: 1.5.3 (2018.4.29f1), 2.1.3 (2019.4.15f1), 3.0.1 (2020.1.14f1, 2020.2.0b13, 2021.1.0a7)
Not reproducible with: 3.0.3 (2020.1.14f1, 2020.2.0b13, 2021.1.0a7)

Notes:
- These are the Components and properties which have this issue:
TextMeshPro - Text (UI): Text Style, Font Style, Vertex Color
TextMeshPro - Text: Text Style, Font Style, Vertex Color
- Additionally, these properties cannot be reverted by right-clicking on them
- Opening the Overrides drop-down list on the instanced Prefab will indicate that the changes were made even if it isn't shown on the property itself