I lost all of my diamond gear when the last update came out because they had fucking mobs respawning in lit caverns for a little while. A creeper snuck up behind me as I was mining and exploded without warning, dropping me down into some underground lava lake. Apparently there was a glitch where you didn't drop items when you got killed, but it didn't matter anyway because all my stuff would've burned up.
They've since fixed both of these things. The respawn thing was intentional, but didn't work primarily because the sound is broken --not only do the mobs not always make sound, but when they do, the sound isn't directional, and it might even be coming from behind a wall somewhere. This is especially irritating when the most silent mob EXPLODES and smashes the landscape. It wasn't fun. And I expect it'll come back at some point, unfortunately.