After clearing Soulfire Bastion and gambling souls I accidentally gambled an item that didn’t fit in my inventory. It vanished into nothingness so I went to stash some stuff before trying any more. Upon transferring my crafting items all the items I put in storage suddenly duplicated in my inventory and it appeared I could put them in storage too.
I then tried to drop some of them on the ground, and they vanished only for the gloves I gambled on to appear instead. I closed my stash and inventory and reopened them again, and the dupes were back in my inventory again, but could now be dropped properly.