Minecraft wiki entry for Development_versions, associated text: [MC-5711] Redstone torches attached to the side of a block do not pop off if the block supporting them is destroyed.
[MC-5721] Dragging to spread an item out in the creative inventory, then clicking on the inventory tab, and placing the 0 stack item down, the game will crash.
[MC-5728] Infinite loop caused by subtraction mode comparators causes the world to be unplayable.
Mineral duplication: you can exponentially dupe minerals by putting then in a crafting table with a block of their material, then double clicking on a mineral in the crafting table, works on the same principle as the method below.
Crafted item duplication: Any stackable crafted item can be duplicated by setting up its recipe in a crafting table, then double clicking an existing version of this item in the inventory. Requires at least one of that item to be present in the inventory.