How to reproduce:
1. Open the user's attached "LayoutGroupPrefabBug" project
2. Open the Scene named "Scene"
3. Select the "Panel" GameObject (child of the "Canvas" GameObject)
4. Check the Control Child Size Width property

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: 2018.4.29f1, 2019.4.14f1, 2020.1.13f1, 2020.2.0b11, 2021.1.0a5

Notes:
- These are the Components and properties which have this issue:
Canvas: Pixel Perfect, Additional Shader Channel
Text: Raycast Padding
TextMeshPro - Text (UI): Font Style, Vertex Color
Image: Raycast Padding
Raw Image: Raycast Padding
Rect Mask 2D: Padding
Layout Group (both Horizontal and Vertical): Control Child Size, Use Child Scale, Child Force Expand
Rect Transform: Anchors (Max value only)
- 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