Farmed Duriel T4 with the partner in the party. Both saw 2GA Mythic Polearm. Inventory was full, teleported to the town, sold items, and went back to the lair (no disconnect/relogin), part of the untouched loot disappeared, including the Mythic item.
next time, when Mythics drop, toss out a couple of crap Uniques to make room.