Any item within an inventory, when dragged from or to another interface such as a crafting table or furnace tend to disappear for a couple of seconds, causing other items to be crafted instead of what you wanted to be made. The items that disappeared do reappear, but tend to at the last minute. This does not happen every time you move items, but it is frequent enough to make me think of it as a decent-sized issue. A single example of this situation is placing two sticks and three diamonds into a crafting table to create a pickaxe, but one diamond disappears out of the crafting table, causing you to accidentally create a diamond hoe. Within a couple of seconds, that diamond will reappear, but alone. Furnaces do the same thing, but you can simply exit and replace the items. Anvils tend to bug out the same way, causing items to end up in the wrong spots or back in your inventory. The anvil issue has been around since 1.6.x.