Flagstar Bancorp held a portfolio of $1.56 billion in interest-only mortgages at the end of 2011, with payments for many of the borrowers set to double in the coming years. A year ago, officials at the bank were touting its efforts to work with borrowers to limit the payment shock that kicks in when IOs reset and they have to start repaying principal. While those efforts continue, Flagstar has also sold more than half of its IO holdings, seeing strong demand from ...