Not exactly a system break, so calling it a bug might be inaccurate, but it still prevents the use of the drones without cheating them in.
The recipy for the drones require engine unit, but in my game (+angel bobs) the item does not exist. it cannot be crafter, and as a result drones cannot be crafted either.
I think that angels industries is the guilty mod for that as it adds alternative engine block item, but there are likely to be other mods that could do that.
