It's weird because it doesn't happen in every household, or the effects are less noticeable. It also seems to depend on the action they are doing. With my painting/writing at-home club, the painters hardly leave the easels at all until they finish a painting. The writer jumps up constantly to go to the toilet or do other things. In another household, one Sim was constantly trying to sleep, but her husband never did. At first, I thought it was because she's lazy and didn't connect it until it happened in another house. This leads me to think that the toilet bug is also somehow happening because of the way the game pushes club activities.