Use Inge's Stay Things Shrub http://drealm.info/simlogical/sl/Sims2Pages/Sims2_MiscHacks.htm (about halfway down the page) to make the furnishings stay and not get sold when they move out. You need to activate it by placing it on the lot then click on it and choose to leave furnishings behind on move out.

Really does sound like you need to try moving them in and out.

Did you look under Fix on the bat box? Forcing errors is not necessarily the only thing that you can do to try to debug a lot. Also, try taking out InTeen if you have it. It seems to be the cause of random lack of free will for a lot of people.

Edited because I can't spell.