Wrong villager trades can happen, such as Stone Masons selling Cartographer trades

I started a creative world, spawned somewhat close to a village, and created a fenced area with roof. I then placed 5+ Villager spawn eggs, then a Zombie Villager to zombify them. I threw splash potions of weakness and gave Golden Apples to cure. While curing, I placed a bed and stonecutters. Strange things happened: Two villagers with Stone Mason job/skin are selling incorrect trades. One of them sells Toolsmith trades (Axe, Bells), the other sells Cartographer trades (Empty Maps). I'm unsure how to duplicate this glitch, so far I'm unable to do so, but it might be worth mentioning.