my villagers are magically disappearing

https://mojang.com/2014/06/minecraft-snapshot-14w26a/

If you are updating from 14w26a or 14w26b, your saved world has corrupted blocks and it will be heavily damaged once you open it in 14w26c. Please use a world backup that was saved with a pre-14w26 version.
Never use snapshots without first making backups of your saved worlds.

I've had this issue in 14w32d and again in 14w33c. Both times when I upgraded (from 14w21 and 14w32 respectively) I've had several villagers disappear without a trace.

I have them disappear and as far as I'm concerned I have not upgraded, unless it does it automatically.

mine do the same thing.. have a bunch and each day they disappear until there are none ... new world each time ..I cure the zombies put them in the village they breed next day gone ..If you ever get a answer i would like to know also why

This is a very broadly discussed topic, so hopefully these things were already considered, but...
...were the villagers in a completely lit and inaccessible area? (wooden doors should be treated as open doors, and one-block high openings are not safe, even adjacent to a wooden door to "block" it, as kid zombies can still go through)
...were there enough villagers for a zombie siege to occur? If so, zombies can spawn INSIDE well-lit areas, including inside houses, and will in most cases the resulting zombie villagers despawn before you return to the village, leaving it empty (unless they fail to kill the golem, which happens sometimes, but they usually get all the villagers).

Of course, neither of these should kill them off if the village chunk itself is unloaded. As for whether a zombie siege can occur beyond the 128 block despawn distance, I'm not sure.

In my case, the last update took care of it. Villagers no longer are disappearing. However, I have never seen zombies appear in well lit areas, if you say they do then at least in my case, I have never seen them. I had blocked the entire village or villages (I did at least four), and in all where disappearing. I repopulated them and guarded them. While playing no zombies ever entered (well lit and even had iron golems protecting); they would still disappear when I exited the game and came back to play or changed difficulty level). With the last update, all villagers remain in their village and although I may exit or change difficulty level, they remain there. So for me, all was taken care of.

Ah, I see. Glad your bug is fixed! And yeah...that sounds even more annoying than the one I mentioned lol...

Sorry to bug you by posting here. The issue may have been marked as "resolved," but the comments didn't reflect that, so I assumed it was "resolved" and not RESOLVED...if you know what I mean.