Renaming with anvils doesn't work

What I expected to happen was...:
to rename my pickaxes and sword with my anvil

What actually happened was...:
the "_" infront of the name in the top section didn't appear and when i cliked on it notghing happend, i tried just typing but coulden't get it to work.

Steps to Reproduce:

• put down an anvil
• get an item, any item
• try renaming the item
• there you have it, you can't rename it

p.s. i have a texture pack so the white shine is not a bug