'Untraded' villagers keep their profession after breaking their workstation

After I broke Villager's workstation before trading anything with him, his profession remained. Even if I broke all workstations in that village, every single 'untraded' villager had its profession from workstation I built but after the spawned workstations were broken, their profession reset. I don't know how to describe it better, but I thing this is enough info about this bug (if it is a bug)