Whenever the villagers sleep, they slide across the ground, and will even rocket away and/or teleport somewhere. One appeared in a water elevator, or even in a bed inside the house (we keep them in a pen outside blocked by a fence), and sometimes even out into the ocean. They don't seem to die, but just teleport back soon after. I also noticed a pig teleporting similarly to the villagers, although clearly not linked with sleeping in a bed.