Just lost a villager to starvation with this issue. I was in slice so I did not notice them standing around the top of the mountain. They randomly teleport from any sitting place or sleeping place within the underground structure. I was developing a dwarf fortress kind of habitat and noticed many missing around day 28.
Bug user ID: c15fd1ec-de56-11e4-a32f-c86000a3795e
Current workaround is roll call in the mornings or after meals. I put all the villagers in one group and post attack orders to ensure all are present and accounted for. However; with the nature of the game this will not be practical with hundreds of villagers.