How to reproduce:
1. Download and open user's attached project "bug04.zip"
2. In the Assets folder, you will see two models "Human" and "Blacksmith"
3. Press on Human Prefab and configure Rig - for Animation type use "Humanoid" and for Avatar Definition use "Create From This Model", check on "Optimize Game Objects" option and click "Apply"
4. Now press on Blacksmith Prefab and configure Rig, for Animation use "Humanoid" and for Avatar Definition "Copy From Other Avatar" and pick HumanAvatar defined in the same Prefab Human.fbx and click Apply
5. Notice that Rig tab does not have an option "Optimize Game Objects", inherited from copied avatar definition
6. Place Human Prefab and Blacksmith in the Scene

Expected results: When placed on a scene Humanoid Prefab Model "Blacksmith" has an Animator Component attached and configured to use provided Avatar model

Actual results: Humanoid Prefab Model "Blacksmith" is inserted in the Scene it does not have Animator Component. You have to manually create Animator Component with "Add Component" button. And you have manually configure it use right avatar.

Reproducible with: 2017.4.11f1, 2018.1.9f2, 2018.2.8f1, 2018.3.0b1