When loading a previously created world from 1.8.3 that I know works, I found all my entities'(non-player,non-fake) scoreboard variables were no longer existent. Upon using the "/scoreboard players list" command, I found all of their entry names, which are their UUID's, had been trimmed from the original 36 character length to only 16 characters, preventing them from being recognized as the entities. This is a very, very big glitch that will break most 1.8 adventure/minigame maps, including those on realms, and should be fixed right away.