Blueprint Macro Libraries based on Actor cannot be reparented to Object

Blueprint Macro Libraries based on Actor cannot be reparented to Object

Reproduced in 4.7.6, 4.8.1, and Main (//depot/UE4/Promoted-CL-2605171)

1. Open any project
2. Create a new Blueprint Macro Library based on Actor
3. Go to Class Settings->Parent Class
4. Search for "Object"

Result:
The Macro Library can't be reparented to Object.