When forging, sometimes I already know the amount of resources I need, so I grab the exact amount first. Once holding those items, you can click the forging item you want (say bolts) but then you cannot deposit the stack you were holding into the forge resource slot. You can take your stack and move it to a spare slot in your inventory, then close and read the specific forging item, then place the slot, but it seems like it should allow for either style of deposting.