From the Minecraft.net site:
Minecraft is a notoriously stable and precision-crafted game. Everyone knows this. However, on the rarest of rare occasions, a tired developer’s finger slips on their keyboard, or someone drops their cinnamon bun into the Central Flux Capacitor, or we forget to make the timely sacrifice to Omak’katheth, and the game wigs out completely. Sorry about that.
But it doesn’t always turn out badly: many of Minecraft’s most infamous errors were, in hindsight, happy accidents, that led the way to new features and even new mobs.
And so, in memory of those fleeting moments of instability and/or serendipity, we asked the developers to recall their favourite bugs and glitches from across Minecraft’s history and its many platforms.