Villagers Dissapear

I herded all the villagers into a chapel and blocked off the door. There was no where for them to go. One day, they were just gone. All of them. The only thing I can think of is that I had just recently added several "buildings" outside to cause them to multiply. The room they were in was 3 X 7 and I only had 21 active doors/buildings so the max # could only be around 7 or 8.

I don't know where they went. I knew they disappeared because I couldn't hear them one night.

What other info would help? I've saved the game just after it happened and I know the seed number.