When a slightly used weapon with several enchants (from Enchanting table) is placed in an anvil with an additional weapon enchant book, the new item shown does not have the enchant on it, but pulling it out of the anvil will consume the book and XP cost

I expected that the anvil would add the additional enchant upon pulling the new item out, the sword retaining its then-current level of durability, the book and XP being consumed. Failing the ability of the anvil to utilize an enchant, I would expect to not be able to pull an item from the "new" slot of the anvil at all.

What actually happened: My XP was charged according to the amount stated in the anvil, and the book was consumed, but the anvil never sounded and the original item was pulled out. Logging out and in did not restore XP or books. The diamond sword was unnamed and had several enchants on it (Bane of Arthropods IV, Looting II) as well as 75% or higher durability. The enchant books used each time were Sharpness (IV and III respectively)

Steps to Reproduce:
1. Craft and enchant a sword at the enchanting table.
2. Use the sword until about a quarter of its durability is gone
3. Attempt to combine this sword with an appropriate weapon enchant that is not on it - by crafting enchanting books and obtaining the necessary XP
4. Place the sword in the first input on the anvil, and the book in the second
5. Mouse over the new item output, revealing the original item unmodified
6. Remove the item
7. The book and XP will be charged and lost.

This should be improperly working. The anvil should be able to add enchants to items despite their durability, and it should not consume material/XP components without imparting any effect.