When having a villager in a minecart run off rails and onto a block so the minecart stops and you retract the block they are on with a piston to drop them to a rail below the minecart will go on it's way but leave the villager behind. This is not just a visual glitch as the villager can be traded with but will never move from floating above that removed block and if you go to where the minecart has traveled no villager is in the new location, you can even enter the minecart. However upon returning to the floating villager he has vanished and is not at the new minecart either.