Witch Huts created in my world (originally generated in 1.6.2) no longer spawn witches after the 13w37b update.

A large, 2 tier, piston floor witch farm farm created on the site of a witch hut generated in 1.6.2 will now only spawn ordinary hostile mobs when the world is loaded with 13w37b snapshot. If the world is loaded in 1.6.2, the witches still appear. From this, I can only infer that the witch hut's location is not part of the save file, but rather, part of the world generator algorithm.

For special structures that have already been created by the world generator and loaded into a chunk, please save their locations in the save file, so that these structures are not lost upon update.

There was a similar issue created regarding Nether Fortresses under 13w37a, but the issue has not been resolved for Witch Huts.

The screenshots below show the view of the output from the witch farm while running under 1.6.2 and 13w37b.