Component hierarchy is reset for a Blueprint instance's newly added components if root is created in C++

When a Blueprint is based off of a class that has its root component defined in C++, any components added to an individual instance of a blueprint reset their hierarchy so that they are always attached to the root component when they are deselected. This does not occur if the root component is defined in the blueprint itself.

Regression?: No
This also happens in 4.16

1. Download the attached project, generate project files, compile, and open the project
2. Drag an instance of TestBP into the level
3. In the Details Panel, add a Scene Component
4. Click and drag the Scene Component on top of the TestComponent to attach it
5. Deselect the TestBP instance in the level and reselect it
   Result: The Scene Component is attached directly to the root again
   Expected: The Scene Component is attached to the TestComponent