It took me forever to figure out that the three repair-items can't be stacked, but have to be spread out.

Have you ever seen a recipe that uses stacked items in a crafting table? '-'

Now that you meantion it... I must have made way too many machine-recepies in AE. Still, it's somewhat unclear.

But it is a vanilla thing, normal crafting operations never used stacked items.

ಠ_ಠ