specialPrice NBT tag works wrong

For example, this command:

/summon villager ~ ~ ~ {NoAI:1b,Offers:{Recipes:[{buy:{id:emerald,Count:5},sell:{id:apple,Count:10},specialPrice:-1}]}}

summons a villager with an offer [-4- 3 emeralds → 10 apples] instead of [-5- 4 emeralds → 10 apples].

This bug doesn't appear in singleplayer.