I had 12 cobblestone and 12 vines, and ended out with 14 mossy cobble

I used 10 cobble and 10 vines to craft 10 mossy cobble, then used 2 cobble and 2 vines to make 2 more, but the vines weren't used until I manually crafted it,

Steps to reproduce:
Have a low amount of vines and cobble in your inventory

Use your crafting book, the side thing, to craft them