Basically, when I kill an Enderman, nothing drops. And I know that Endermen don't always drop pearls, but when you kill around 22 in Survival mode and nothing happens, I think it's safe to say that there's a bug. I went into Creative mode and spawned tons of Endermen & killed them all with a Looting III Diamond Sword and I got no pearls. I even tried Endermites and nothing happened.