Retracted pistons and glass are considered block normal cubes

Mobs can spawn on regular ice

Dispensers cannot dispense Jack O' Lanterns to create snow/iron golems even though the player can

When any non-player entity enters an End portal the obsidian platform is not regenerated and the entity can fall into the void

Entering a nether portal in Debug Mode makes the "Downloading Terrain" message appear infinitely

Player clones when logging in and out of MC (servers) fast.