Blue highlight is missing on making changes in Target Sorting Layers of Light2D prefab

Steps to Reproduce:

1. Open attached Project
2. Select Hierarchy > Sprite Light 2D > Inspector > Light 2D > Target Sorting Layer > None

Expected Result:
Blue highlight appears on the left border of the Target Sorting Layers

Actual Result:
Blue highlight is missing on making changes in Target Sorting Layers of Light2D prefab

Reproducible on: 2020.1.0a13, 2019.3.0b10, 2019.3.0b4

Environment: Windows 10 and Mac 10.14

Note: URP as a package has been introduced in 2019.3.0b4