Same here. It only happens to the family that are in the house I built myself. My other sim that i play in the same save doesn't have the problem and they're in a pre-made home. I think each house has a different front door. Also it doesn't happen all the time; yesterday I was playing for an hour before it started to happen.
SimGuruGraham is aware of my problem; I informed him of it in his 'ask a SimGuru - afternoon edition' thread. He said that it was a 'strange one' and asked me to upload my house to the gallery for him to take a look at. He hasn't took a look yet, as I know of (he hasn't been on twitter and that's where he told me to send him pictures of the house as well).
Thanks for the extra info
