The upkeep has to be unpaid for more than 180 days before they will be foreclosed.
That's now the only requirement.
If you know of any houses that have unpaid upkeep longer than that then I would suggest you submit a ticket to Turbine. I can't say if they will do anything about it, but it's your best bet.
[center][url=http://forums.lotro.com/showthread.php?18699-How-to-get-help-on-the-Tech-Forums-and-how-to-contact-Turbine][color=gold]How to get help on the Tech Forums and how to contact Turbine[/color][/url]
[color=green]Please reply to the topic or PM me if a solution I posted works for you: The more data I can gather the better I can help.[/color][/center]