Adult Villagers despawn?

I spent hours in my Minecraft world moving Villagers by minecart. I got the two Villagers where I wanted them, I started breeding them. I got two baby Villagers, then my game crashed. I logged back in and my two adults were gone but the babies were still there. I hurried and named my other two villagers with a nametag (by this time one of the baby villagers where grown up and the other was still a baby). Once again the game crashed and my adult was gone. I then tried seeing if trading would make them say and that seemed to work, but 3 villagers despawned! I thought they were not supposed to do that! 

Maybeme