This issue can be prevented by downloading and installing The Sims 2 Patch.
I have this patch, it still occured.
Well, obviously, the EASY answer is just to drag it up and down in debug mode, but that's not an answer you can give to sheep.
I was on my way to do this, but the problem became easier to solve. All I had to do was re-enter the house. The sim seems to have reset himself.