Hello Gingerkid,
I have noticed this since IP, but, do not have a solution, sorry. Prior to IP I was in the habit of moving a family in France, complete with their house to another lot because I just happen to like their lot for building my sims' vacation home. Since I installed IP, and after several crashes, I have had to evict the family, place them in another existing home and then bulldoze the lot so that my sim can purchase it. I don't know if you could achieve what you want to do by using the same method.