Hi Mojang,
Recently I noticed mobs dropping strange items in my worlds recently. Here's a quick list of things they drop that they're not supposed to drop:
Ghasts occasionally drop Ender Crystals when you deflect their fireballs back at them.
Bats used to drop TNT in one of my worlds when they flew through lava.
Today I noticed a creeper that took a lot of hits to destroy with a diamond sword. When I finally destroyed it, it dropped a full set of diamond armor plus a diamond sword.