Villagers Despawning

I am in a vanilla server, and a tried to make an iron golem farm. i got to 14 villagers and it started working. I left my house and went to spawn, when i got back there were only 8 villagers. I got to 14 again by trading and trowing bread. Same happened. I ignored it and waiting to get fixed on the next snapshot. I only have 3 now.