Applying a material to an actor in UE4 prevents deletion with Datasmith

Hey everyone,

Our team noticed a bug with Datasmith recently and it’s shown in detail in the attached image. I’ve confirmed this exists in 4.21 with all current exporters. Steps to re-produce are as follows:

1.) Create object in Max, can assign a material or leave blank.
2.) Export DS file and import into UE4.
3.) If you now delete this object in Max, re-export the DS file, re-import in UE4 the object is deleted as expected.

If you assign a new material to this object in UE4 after step 2 above, then try step 3, the object is NOT deleted.

Now obviously, if we assign a new material to an object in UE4 we want that material to stay if we are editing that object in Revit/Max. But we do not want that object to be immune from deletion. For example, if we are working with a Revit model and we assign our nice PBR materials to a wall in UE4, then an architect removes the wall in Revit due to a design change, we need Datasmith to capture this change and properly delete the object in UE4. We have many architects working in the model simultaneously and it would be impossible and impractical to track what’s getting deleted by hand, we need DS to handle this.

Can anyone confirm this is a bug? If this is intentional behavior, how are we intended to deal with dozens or hundreds of objects that should be deleted and aren’t?