Urn does not turn into tombstone

I have a urn of my dog in my inventory and want to place it outside so i can turn it in to a tombstone but everytime i place it outside it turns into a urn and i cant change it.

I tried restarting the game or using "bb.moveobject on" to maby place it and let it stay a tombstone as shown in my inventory but nothing helped

I can put it in to my inventory and move it to the world but as soon as i drop it always turns in to a urn