Villager changes profession or trades after being traded with

when I was  trading with this farmer villager i got its trade levels up to 3 because i needed apples to make golden apples but as soon  i ran out of emeralds , so i opened my enderchest to get more. as soon as i tried to trade with my villager it changed it profession from farmer to a fletcher even though there was no work site job for making this villager to a fletcher and the farmer worksite  is literally next to the villager. so now i have to get a zombie villager, cure it, make it into a farmer, to get more apples.Minecraft devs please fix this bug.