I'm not sure about the bug, it might just be back or a bad seed, but it happens most often between 1.8.3 and 1.8.7. The bug involves when someone changes their skin and you have a player head. If the head updates before the world loads, the old skin is stored in a random part of the game or deleted. If the world loads before the head updates, the new skin is stored randomly. If it gets in the level file, it will cause corruption. I think this is true because the more heads I had, the worse it would corrupt.