When placing an enchanted book and an item into an enchantment table it is possible to reforge and item multiple times with the same enchantment or many different ones and cause the anvil reforge cost to reach millions in creative mode. what should happen is it should prevent reforging if the item already has the exact enchantment of the same enchantment of a lower power

To test simply put an item in the first slot of an anvil and an enchanted book in the second slot, doing this over and over with the same enchantment will still cause the cost to increase.