Villagers spawn only a single type

What I expected to happen was...:
Villagers spawning of different types (farmer, librarian, ect.)

What actually happened was...:
Villagers spawn only with the normal, non trade-able, typing. Biome variations still spawn accordingly. Villagers occasionally randomly become the farmer typing after being normal typing. Happens both in singleplayer snapshot and multiplayer snapshot. Both natural villages, spawn eggs, and /summon have this problem.

Steps to Reproduce:
1. Launch Minecraft Snapshot.
2. Find a village or spawn villagers.
3. The villagers will spawn only in the normal typing (with the exception of an occasional farmer type).