Villagers in minecarts fall thru farmland when rails are below it

i had a villager traveling on a minecart. as he reached my farm, a rail was suspended 3 blocks over the farm, which would force him to fly and land on the farmland. when he hit the farmland, he went thru and landed on the rails below. his head was moving back and forth thru the dirt, and was not taking damage. the point is he should not have gone thru the dirt.