When I was playing on my survival world, I decided to take my Efficiency 3, unbreaking 3 shovel and upgrade it to efficiency 4. I took a efficiency 1 book put it in the anvil with the shovel and it would not combine. I then looked it up on the Minecraft Wiki and it says that you can get up to 5 levels of efficiency. I then made the book efficiency2 and then tried to upgrade my shovel. Nothing happened And I was putting everything in the right order.
The Bug:
Cannot upgrade items to next efficiency level with enchanted books.
STEPS to reproduce:
Enchant an item with an enchanting table.
Grab a book to upgrade it's enchantment level.
Try to combine them in a anvil.
This is intended behaviour. You need to use a efficiency IV book to make it efficiency V.