In Creative mode.

After using every spell book possible to max out the armour and leggings, the anvil won't allow me rename them. I can type the name in, and recover them (un-renamed) from the left hand box, but it won't let me drag ithem out of the right hand box. Also, the green "enchantment cost" text won't appear.

Quitting and restarting doesn't help, and I can rename other maxed out objects such as the helmet, sword, shield and boots.

Renaming is possible on all other nameable items.