The Chewed Corpse placeable on the Fat Rat quest didn't spawn any treasure. I tried opening it a few times, waiting for various lengths of time, before giving up.
Considering it's the only treasure on the quest and the rat can take out a bit of your HP, this is a bit disappointing.
I think a few weeks ago a similar bug was reported, regarding all three refuse piles on the Bat Tower quest, BTW.