OMG finally there's someone else with this problem. I built a house for my sim family of 8 people and so it has a massive kitchen with a lot of counter space. I took one of my adult sims to go to the house of another sim and when I came back, all of my sims (apart from one toddler sim and one child sim) had filled up all of my counters AND THE FLOOR with White Cake or ingredients for white cake and instantly I was like WHAT and I stopped them all from doing that and I made them do other things around the house. However, about 30 seconds later, they had all self-cancelled that and were back to obsessively making white cake. Not joking, it made me want to burst into tears! Heheh :)