Enderman drops up to 4 enderpearls when killed with looting III

I attacked an enderman with my diamond sword enchanted with Looting III and he dropped 3 enderpearls. I then tested this in creative and found the drop rate to be 0-4 enderpearls when killed with any tier sword with looting III. Not quite sure if this is a bug or not, but I suspect it is. Thanks!