This is apparently a high hurdle for some companies to get over, given the intricacies of the mortgage securitization process... so says Karl Denninger.
In any event, there are very specific and straightforward laws that govern the foreclosure process. All we have to do is follow them.
There appears to be a lot of different issues involved with this whole mess.
To me it looks like mortgage companies buy and sell the debt for the interest. My mother unexpectedly paid off the last of her mortgage in one lump sum and triggered a foreclosure attempt. Somebody bought the debt expecting interest to be paid over time. She paid it all at once and someone was left holding an empty bag. The mortgage servicer dropped the foreclosure attempt but her deed is still getting straightened out.