NPC hunger no longer decays

I have been trying to kill NPCs by locking them in a room and waiting for them to starve. According to reddit this can take up to 10 days. I waited ten days and some of the sims have a full hunger bar when I try to play as them.

I made sure none of the sims are vampires, pregnant or have any other way of surviving. The other needs decays as normal except hunger.

Is this a bug or a feature?