BP Assets bleeding into other BP's Thumbnails

When you place a Child Actor into Static Mesh Actor Derived BP then place that BP into another BP of the same class as another child actor, the thumbnails of all Blueprints in your project will included portions of the Final BP.

Also Reproduced in Main Promotable-CL-2593205

1. Open QAGame Editor
2. Create a Blueprint from StaticMeshActor named "A"
3. Create a Blueprint from StaticMeshActor named "B"
4. Create a Blueprint from StaticMeshActor named "C"
5. In "A", Assign StaticMesh'/Game/TestPackages/Misc_Assets/StaticMesh/BeachBall.BeachBall' as the Mesh.
6. In "B", Assign StaticMesh'/Game/Environments/Props/Boxes/Meshes/AmmoCrate_Closed.AmmoCrate_Closed' as the Mesh
7. In "C", Assign StaticMesh'/Game/TestPackages/Misc_Assets/StaticMesh/ChestArmor.ChestArmor' as the Mesh
8. In "B", Create a New Child Actor Component from "C"
9. In "B", Move "C" off to the side so you can see both meshes
10. In "A", Create a New Child Actor Component from "B"
11. In "A", Move "B" off to the side so you can see all three meshes
12. Compile and Save all BPs ("A", "B", and "C")

RESULTS: BP from the entire Project will get the meshes assigned in B and C in the Thumbnail Previews. (If the BP Thumbnails don't show it immediately, you can go into edit Thumbnail mode and it will appear or simply open and save BP again.)

EXPECTED: Not that, other BPs Thumbnails should be unaffected.