When changing a variable of a component in an attached Actor, the variable becomes read-only

Changing a variable of a component with an instance of BP derived from StaticMeshActor or SkeletalMeshActor attached to another actor will cause that variable to be read-only. It did not reproduce with BP derived directly from Actor.

The cause of this bug is that UCSModifiedProperties.Contains (& PropertyAndParent.Property) in SActorDetails :: IsPropertyReadOnly is true. For ordinary flows, UCSModifiedProperties should be empty at this point. However, UCSModifiedProperties is not empty for conditions that reproduce this defect.

1. Expand the attached file and open AttachedActorProblem.uproject with 4.18.2 or higher UE4Editor
2. Select NewSkeletalMeshActor2 in the WorldOutliner
3. Select Scene
4. Change Auto Activate to true

Note that the Auto Activate property is now read-only.

Relatedly. If you Select NewSkeletalMeshActor in the outliner, and select scene and set auto activate to true, then the auto activate property of NewSkeletalMeshActor2's scene component becomes true.