If the vanishing villagers are a doctor problem, here's something weird I've noticed about the doctors--this is after you have a lot of villagers. When you first start the game, you'll usually find everyone off doing their own thing--except for some of the doctors. A few always seem to be frozen in place. If I move them a little, they come back to life, but otherwise they just seem to stay there, doing nothing and not moving at all.

I have a Palm Tungsten E.