While my friend and I were playing the snapshot, we found a bug that duplicates items. Using the "f" key to place an item into your offhand slot actually duplicates the item. Even more issues arise when you use consumable items like potions and food, allowing you to obtain negative amounts of an item. The process goes like so:
Step 1: Get a consumable item (splash potions work very well, and very quickly)
Step 2: press f to duplicate the consumable to your offhand slot.
Step 3: Consume the item. (Note: This will crash your game, and causes you to have 0 stacks of the item.)
Step 4: Consume more of the item. This lowers the item count into the negatives. (Note: Clicking any of these "duplicated" or negative count items makes them disappear.)
Step 5: Consume the item until you have -128. Consume it again will bring the count to positive 127. (Note: Throwing the last item in the stack after having it count down from 127 will crash the game again and restart the cycle.)

On a side note, pressing f when you an item in the offhand slot, and nothing in the main hand slot will not move the item.

Credit to NebulaeDragon for finding the infinite item cycle glitch, after I found the offhand slot duplication glitch.