When Crafting from Metal Block form to Ingot or Diamond, with a partially full inventory there is a possible factor for losing said material. As you can see in the attachment, i have 8 slots free in my inventory, I Shift-Click the iron blocks out, and i am left with 7 iron blocks, rather then the 8 i am supposed to have, The next photo is when i finally uncraft those blocks, you'll notice i only have 63, cheated by one iron. Also, lost can be much higher depending on how full your inventory is.