Or, charger42 is old skool and still refers to everything as OSI, even though EA has owned it since it's beginning, and he's really just asking about the normal IDOC cycle. I'm not sure he's talking about houses that have gone "Owned by OSI."
The co-owners and friends lists are not cleared during the decay cycle. They can still access the house and if any co-owner had locked anything down they should still be able to remove it. Sounds like somebody went in and removed their stuff from a decaying house.