I'm going to weigh in here on what I know. Take this with a grain of salt, it's only from reading and direct observation.
Owned by OSI occurs 2 ways (that I know of)...
1) An account is banned or has some action taken against it and the case is not "closed" on the matter. I've not been banned yet (*knocks on wood*) so I don't know the process but I've heard of people getting unbanned so there must be some appeal process that exists. During the time the account is banned I'm assuming the credit card on file isn't charged so the account goes delinquent (im assuming here) and the house begins to decay. When it would normally fall it goes to OSI status ie "pending"... but as far as I can tell once a house enters that status, they have no code to update it once the case is settled. I may be way off on that but it's how I like to think of it and it seems to make sense.
2) If you've got a vendor house who's parent account is closed, EA can't just let the house drop because the vendors (attached to the sign) would go poof along with all their items, hardly fair for the paying customers of EA. Solution, when a house IDOC's with others vendors still inside, it goes to OSI status. This is to allow the vendor owners the ability to remove items / gold and possibly even the vendors themselves. If the gold the vendor is holding gets used up through vendor fees it will eventually fall and so should the house after the last vendor is gone. What I'm unclear about is if once the last vendor falls if the house will drop instantly, complete the predicted IDOC schedual then drop or get stuck in the perma-OSI state like in the first example.
As Xclio mentioned, a post was published in UOHerald a short time ago asking people to report the locations of old OSI houses via an e-mail to a specific address with shard, facet, coords, house name, etc. It was mentioned the houses would be manually deleted at random times by GM's and would not follow the normal decay cycle. What wasn't clear is the fate of the contents... I suspect the contents of the house fall upon deletion but I've never witnessed it happening nor have I come across a plot with IDOC loot that was formerly occupied by an OSI owned house.
Over the years I've had many full books of OSI owned houses, some have stood for many of those years so my advice is forget about them, spend your resources and time searching for new IDOC's that will drop at a predicted rate. Perhaps check them once a day for the land plot if you're adamant but don't count on getting these items. When I attend an IDOC and it flips to OSI, I walk away and re-write the rune with a new non-osi decaying house.
My $.02
-K
