Heirlooms give Sims an Angry "Dead to me" moodlet whenever they view it, even though they had a good relationship with the deceased Sim, and also in the case they did not even know the deceased Sim. ...
Ideas
Wanted to add: Before the deceased Sim has moved on, the Sims viewing the heirloom still get a positive moodlet when they had a good relationship with the deceased Sim. So the bug starts when the deceased Sim moves on to Netherworld or Rebirths.