Custom Villager trading

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~~~