Thanks for reporting it to Maraxis. There is nothing in Cargo Ships that could be causing this, to my knowledge. The sub-entities are indestructible and un-collidable, so they have to be getting deleted by a script somehow. Cargo ships deletes them when the oil rig itself is destroyed (the mining-drill entity). Either Maraxis is removing the sub-entities without removing the main entity, or it is destroying the main entity and then rebuilding it with raise_built=false so Cargo Ships never gets an event to add the sub-entities.
