The default scene root of an blueprint actor is not removed after adding a static mesh component via C++ until after restarting the project

The default scene root of an blueprint actor is not removed after adding a static mesh component via C++ until after restarting the project (or reloading the blueprint asset)

Found in 4.22 CL#7053642

Reproduced in 4.21 CL#4753647, 4.24Main CL#7206954

1. Create a new code project.
2. Create an actor C++ class and create a blueprint actor from it.
3. Place the actor into the level and save everything.
4. While the project is still open, in the C++ actor declare a UStaticMeshComponent and initialize it in the constructor.
5. Compile the code.
6. Once compile is complete, select the blueprint actor in the level.

RESULT

In the Details panel, the static mesh component is added to the component hierarchy and DefaultSceneRoot is nested under it.

EXPECTED

The DefaultSceneRoot to be removed.

WORKAROUND

Reload the blueprint asset. This will remove the DefaultSceneRoot.