I caught a Zombie-Villager with the help of a minecart and purified him with a splash potion of weakness and a golde apple.

After the transformation, the newly created Villager was not in the minecart. instead it got teleported to the place where the Zombie was originaly picked up by the minecart.

The bug can be reprodruced, I made the error 3 times before realising that the villagers got simply teleported back.

The Zombie was standing on a fence post when he was picked up, as the result of a spawner-trap.