Duplicate nested prefabs are created when adding any component to CBA nested prefab.

Steps to repro:
1. Create new project.
2. Create CBA nested prefab like
'A' instance has 'B' child and 'B' has 'C' child
'B' instance has 'C' child
'C' instance stays without children.
3. Open 'C' asset.
4. Add component -> Video player" Component (or any component)
5. Back to main scene.

Actual Result:
In the hierarchy, 2 instances of B and C is created.

Expected Result:
The hierarchy should not have 2 instances of B and C.

Reproducible in:
2019.1.0a7, 2018.3.0b9, 2018.3.0b7

Working Fine in:
2018.3.0b6

Environment:
Windows and Mac.