Corpses are not always stacking properly
Two similar corpses go in different stacks if one of the corpses has been rotten and uncursed and the other has not been previously rotten (but is uncursed). Most likely this has something to do with rotten flag not being cleared when corpse is uncursed.
How to reproduce:
- Find an uncursed jackal corpse (or any other corpse should work as well).
- Let it rot to cursed.
- Cast remove curse on the corpse.
- Find another uncursed jackal corpse. Now these two corpses are in different stacks.