Blue highlight is missing from "Initial Event Name" checkbox is selected in the Prefab

Steps to Repro:
1. Create a new Project
2. Install VFX from the Package Manager
3. Hierarchy > right-click > Visual Effect > Visual Effect
4. Create a prefab of Visual Effect
5. Click on Hierarchy > Visual Effect > Inspector > Initial Event Name

Expected Result: Blue highlight should be available on the right side of the value

Actual Result: Blue highlight is missing

Reproducible on: 2020.2.0a18, 2020.1.0b16, 2019.4.3f1, 2019.3.15f1 with Package Version 9.0.0-preview.33, 8.2.0, 8.1.0, 8.0.1, 7.4.1, 7.3.1.

Environment: Windows 10 and Mac 10.15