After two years of significant improvements, the total past-due rate for subprime mortgages has stalled since the first quarter of 2012. Special servicers continue to grow their subprime holdings in an effort to work out the poorly performing mortgages. The total past-due rate for subprime mortgages at the end of the fourth quarter of 2013 was 20.82 percent, according to the Mortgage Bankers Association, up from 20.14 percent in the previous quarter and from 20.30 percent in the fourth quarter of 2012. The past-due rate on subprime mortgages peaked in ... [Includes one data chart]