When you deactivate a Spider Spawner with torches, so that no spiders spawn, you get skeletons spawning, all facing north and not moving, within 4 blocks of the Spawner. see attached screenshot. Removing torches and then re-logging removes them again!
Environment
Windows 10, Java 1.8.0_25 64bit, 8x intel core i7 cpu 2.4ghz, 8GB ram
This issue duplicates MC-89923