Blue highlight is missing on changing Mode property in Custom Volume Pass prefab.

Steps to repro:
1. Create a new HDRP Project.
2. Hierarchy > Right Click > Volume > Custom Pass > Create its Prefab.
3. Select Custom Pass Instance > Change Mode property.

Actual Result:
A blue highlight is missing on changing mode property.

Expected Result:
A blue highlight should be appeared on changing mode property.

Reproducible in:
2020.2.0a10, 2020.1.0b8, 2019.3.0f3 with Package version 9.0.0, 8.1.0, 8.0.1, 7.1.8.

Environment:
Occurring on Windows 10 & Mac 10.15