Mob Spawners convert to pig spawners

I started my world in the one of the newer snapshots (50 something). Upon updating my world today my skeleton spawner has changed into a pig spawner.

Possible recreation:
1. Create world in a 1.9 snapshot (earlier than 16w02a)
2. Find skeleton spawner (maybe others).
3. Leave area to unload chunk with spawner.
4. Update to 16w02a.
5. Return to find mob spawner is converted.