I've just tested on a new save stealing from every npc in the fort, as well as stealing a bunch of stuff on the ground everywhere, then leaving and reentering the area and letting the game run for an hour while standing there. Could not replicate the issue on the new save, even though I think I did pretty much everything that I did on the corrupted save.
Seems like its just some random glitch? Or maybe it only happens while in multiplayer, do not know.