How do I make it so items in crafting grid are removed only when the output item is removed?

I may figure this one on my own at a later date, however, I was wondering how to make a custom crafting table that doesn't remove the items in the crafting grid until you remove the item in the output slot. I got the recipes and GUI finished and working, I just want to figure out how to have it feel more like the vanilla version.

(Edit: Nvm, I figured it out. I forgot about the output slot's conditions '-'; )