Singleplayer - if you grab an item and drag it over the crafting table's interface with your middle mouse button, it puts a stack of that item in every slot you go over and the item that you are holding goes into the negative numbers, but as soon as you release it, it disappears.
Meepcraft creative - you got to keep the negative amount of items in your inventory and make operations with them.
https://youtu.be/NIJ4mja4eAE
Sorry, I know this is a laughable at "bug", but I thought it would not hurt to put it up here.
Steps to replicate:
1. Grab a stack of an item
2. Open either the crafting table or E interface for crafting
3. Holding your middle mouse button, drag the stack of items over a crafting slot
4. Put the (-) amount of items back into your inventory
