Virtual Camera Children list disappears on adding/deleting more than one child camera in Clearshot camera prefab in prefab mode.

Steps to repro:
1. Open the attached project.
2. Open "CM ClearShot1" in prefab mode.
3. Add more than one child camera in "Virtual Camera Children" list.

Actual Result:
Child camera list disappears on adding/deleting child cameras.

Expected Result:
Child camera list should not disappear on adding/deleting child cameras.

Reproducible in:
2020.2.0a3, 2020.1.0b2, 209.3.3f1, 2019.2.1f1, 2019.1.0f1.

Tested on Package Version: 2.6.0 - preview.2, 2.5.0, 2.4.0, 2.3.4, 2.3.3, 2.3.1.

Environment:
Occurring on Windows 10 & Mac 10.14.