Minecraft wiki entry for Block_and_item_duplication, associated text: Dragon eggs and anvils fall differently from each other and other gravity-affected blocks such as sand, gravel, and concrete powder. Neither dragon eggs nor anvils work in a sand/gravel/concrete powder duplicator because of this. However, it is possible to create a machine that can duplicate dragon eggs and anvils but not sand/gravel/concrete powder. They both can be duplicated and sent into the End as either falling entities or items.