RGB, R, G and B button does nothing in Lightmap thumbnail preview

Steps to Reproduce:

1. Create a new Project
2. Create Hierarchy > right-click > 3D > Cube
3. Click on Cube > Inspector > Static
4. Window > Rendering > Lighting Settings > Generate Lighting
5. In the lighting window open Baked Lightmap tab.
6. Shift-click on the first baked lightmap in the list.
7. Click on RGB, R and G button

Expected Result:
Lightmap data should show color according to option selected

Actual Result:
RGB, R, G and B button does nothing

Reproducible on: 2020.1.0a14, 2019.3.0b12, 2019.2.12f1, 2019.1.12f1, 2018.4.8f1

Environment: Windows 10 and Mac 10.14