After leaving the cell of a recently killed NPC I can go back to that cell and find that the inventory of the NPC has refreshed. It doesn't come back exactly the same but instead chooses items from the enemies loot list as if it had respawned.

Any ideas what could cause this?

I've looked at my scripts and can't find anything that would cause this.

Does the NPC have a "Death Item" entry?

Are you using Streamline?

No I dont use Streamline and no death item entries either.