I attempted to combine two Sharpness I books using an anvil. I had the necessary experience and put them in the anvil. A Sharpness II book appeared in the final slot.

When I clicked on the Sharpness II book, I held it for a moment, before it vanished and the Sharpness I books reappeared in their slots. The anvil sound did not play but the levels were still used. The books would not recombine unless I removed one from its slot and returned it there. Upon logging back in, the lost levels were returned to me.

I attempted combining the two books while changing the name of the product to "Enchanted Boo". After changing the name, a Sharpness II book with the new name appeared in the final slot. I clicked on it, the anvil sound played, and the result was a single Sharpness I book with the new name. I also attempted to combine two Power I books with similar results.

I attempted to reproduce the bug in Singleplayer and Multiplayer (version 1.5.1), however the combination was successful with a variety of different enchantments on both versions, suggesting that the bug is specific to Minecraft Realms.