When all enchantments were removed from a purifier, the itemstacks may not be cleaned of nbt data correctly, to be investigated.
It may be the cause of this: Corail31/recycler#1

The problem is solved and didn't come from you, thanks a lot ;)

@Corail31 Ok, no problem.
I'll leave this issue open anyways, because I'm not certain that I actually do this cleanup. It should not cause any problems, but it's not very nice.

One thing it could do is raise the price for re-enchanting the item.

I have now confirmed that the Purifier does not strip the "prior work cost" from the item. I stripped my diamond chestplate of three enchantments, most of them applied in parts and/or from combined books. Trying to re-add Protection IV gave a cost of 19 levels. When I fed it to Corail's Recycler and remade it from the diamonds, the new cost was 4, and I restored all 3 enchantments for 12 or so levels. ETA: This is the 1.9 version

The purifier should not leave any NBT tags on the itemstacks because it uses EnchantmentHelper.setEnchantments which removes the any NBT tags.

Concerning the "prior work cost": I do consider this as a bug and it should be fixed in 1a76807