I had two diamond swords in my inventory, one normal and one with Smite IV on it. I went to the anvil with an enchanted book (Power II, Punch I) and tried to see if I could combine the normal diamond sword and the book's enchantments. I found out it did not work, HOWEVER, I noticed immediately afterwards that the enchanted sword in my inventory was no longer enchanted. Now I have two normal diamond swords.