It's an old bug, it came with /summon
So when I create via /summon a Villager who buys a paper with the enchant 30 lvl 30, with a name & with a Lore, and give a diamond chestplate, he can buy any paper. He can buy a paper without anything special.
I don't know if it's realy a bug, but it's sometime a problem.
Look at the screens !
~~~Thanks~~~
Thanks & sorry I didn't see it :/