Villagers in a typical village containing multiple houses will all crowd into a single house instead of spread out to all the houses.
During day time they will bunch up in one house, sometimes venturing out about 8-10 blocks only to quickly run back inside the house.
Started happening in 0.16.0.
I'm having this issue as well. There are over 20 buildings in the village & 99% of the villagers will cram into the same house at night. Not just any house....The smallest one in the village.