Are you talking about backpack-2.0.1-1.7.x.jar? Let’s see if I can reproduce it.
EDIT
Can’t say I can reproduce this, I tried crafting a robust bronze machine casing with 6 double bronze plates and two long bronze rods + titanium-gold wrench. I placed the pattern in the bags crafting grid and ladders in the first slot of the crafting bag, the other materials in my regular inventory.
I failed to craft anything until I placed the materials in the bag.
Can you confirm what mod you are using?