In many cases, absolutely.
Haven't you been following this? They make payments, , but in many cases the ownership has changed hands so many times there is no telling who the correct recipiant of the mortgage should be.
It has gotten pretty bad.
Yep... the same thing happened in the 1990s with the mortgage portfolios of the failed S&Ls. After the Resolution Trust Corporation got their hands on the loan documents, quite a few borrowers had payments that didn't post to the loan balance sheets. The problem only got worse as RTC spread the mortgages around to third party purchasers (like GE Capital Asset Management, IIRC).
Foreclosures in some states often couldn't go forward because of missing assignments and promissory note endorsements. Sounds like the current mess is the same scenario - on steroids.