Whenever I try to combine 2 enchanted books of the same type to form one of a greater level in an anvil, the product is the same level as the ones I tried to combine. It costs 2 of the same level books and a certain amount of XP yet still gives a product which nobody was expecting. If you keep putting them together, the XP needed after about 30 times combination would be 10 digits long!

Steps to reproduce:
1. Place an anvil.
2. Get two identical enchanted books.
3. Put them together.
4. The amount of XP needed after taking the product and redo-ing several times is unretrievable, even if using commands!