It seems the option "[Trade 6 valuables for an Invisibility Potion]" in this quest is broken; He takes your valuables, but you get no potion. It seems the other options (at least Restorative Elixir, Scavenging Gear and Fortitude Potion) are working fine.
http://img248.imageshack.us/i/scavengingbug.jpg/ <- See the screenshot for details/proof.