The DefaultSceneRoot's tooltip claims, "Adding a new scene component will automatically replace it as the new root", but this is no longer true in 4.8 and 4.9. Instead, the DefaultSceneRoot remains in place and new components are added below.
I believe this is intended, but the tooltip is inaccurate.
Reproduced in 4.8.1 and Main (//depot/UE4/Promotable-CL-2598545)
1. Open any project
2. Create a new Actor Blueprint
3. Hover over the DefaultSceneRoot in the Components tab
4. Note the "Adding a new scene component will automatically replace it as the new root" comment in the tooltip
5. Add a new scene component
The new scene component is added below the DefaultSceneComponent, which remains the root
This behavior is expected, however the tooltip is incorrect
Head over to the existing Questions & Answers thread and let us know what's up.