Zombie villagers bug

I've been playing minecraft beta 1.19.30.21 for a year.
I had 5 zombie villagers nametagged, each one from a different biome: 1 from savanna, 1 from desert, 1 from swamp ecc.
I've always kept them in a plain biome, near my base, therefore not in their original biome where they spawned.
Since I've updated to 1.20.30.21 they look like this
Once I noticed this bug, I tried to cure them in a creative copy of my survival world. When cured, their villager counterpart belongs to their native biome (therefore I had 1 swamp villager, 1 jungle villager, 1 desert villager ecc.)
But if zombified again, the same visual bug comes back.
Cheers