Stephen Ford
Comments
In 1.8, this was changed. Unbreaking can now be found on swords/bows/armour. Prior to this change, it was only possible to apply Unbreaking via an anvil.
Yes, this is not a bug. Check the minecraft wiki on enchanting, and it will tell you how the system works.
Looks to me like lag. If you have lots of cows, that may be part of the problem.
If you have blocks of any sort (torches, carpets, and half-slabs all count) between the bookshelves and the table, you will disable some of the bookshelves, meaning not all 15 are affecting the table