#NOTE - THIS ONLY EFFECTS SURVIVAL# DOES NOT WORK IN MULTIPLAYER#
The anvil will not allow you to combine two enchanted books of the same enchantment in survival.
In the previous snapshot, it was possible to combine enchanted books this way and get a higher level enchantment. (i.e. two sharpness IV books created 1 Sharpness V).
See picture for more details.
Environment
Windows, Java 7 u10
Don't clone open issues.