Oh. I never crafted the backpack, because from its description I thought "well, I haven't ran out of space for anything so far, I'll make it when I'll need it", and then forgot about it. Maybe it could say that it actually unlocks the ability to use new items? I assumed it meant resource capacity, or something I would find eventually and know when.
And if winterheart decreases your mining power, shouldn't that also be said in its description? Or did I just miss that too.
Anyway, thanks for the quick reply and for making this cool game!