Villager goes through half slab

If a villager is standing on a bed and the top halfs of the blocks  two blocks above the bed are slabs, a strange thing happens. If there is a water stream on the slab and the villager takes damage, he goes through the slab. If there is no waterstream, it doesn`t happen. I hope you understood what I mean and I hope I can help you with that  Also thanks for the great job you do in making a game that is sooo great. Bye