I could not google anything about this. when a person dc, he drops items. i picked up shieldbreaker and could not upgrade it. is this by design or bug? sb is good, but when it is stuck at lvl 1, it can be a hinderance late game when more damage is needed
I honnestly have no idea, but you might have more luck in the mechanics forum for this kind of question.
I remember that happening. I think you just wait a few minutes with the item in your stashand then you are able to upgrade it.
You can't stash them, no. If I recall correctly, you upgrade it in the courier. (Once upgraded or used as a component with other items, it will be flagged as your item)