Per-section shadow/collision flags lost when merging actors

Information loss when merging actors such as cast shadow and collision. If one of the actors being merged has a different setting such as not casting shadows. This information will be lost and replaced with a new setting that affects the merged actor as a whole.

1. Open the editor
2. Two static meshes to the level
3. Click on the static mesh in the viewport
4. Turn off Cast shadows (from the details panel NOT the static mesh editor) for only one of the meshes
5. Selected both meshes
6. Merge the actors together (window > Developer tools > Merge actors)
7. Drop a new copy of the merged result in to the level
8. Notice that both pieces are casting a shadow

Expected: The cast shadow information would be retained and only part of the mesh would cast a shadow or that the option for both pieces would be available to turn on and off
Result: The new mesh can only cast shadows as a whole or not at all