Mortgage insurer PMI has sued NovaStar Financial over claims that the lender misrepresented its underwriting policies for stated-income loans. The PMI suit, filed in the US District Court for the District of Kansas, represents the latest salvo in an ongoing legal tussle between the two firms. In December, NovaStar sued PMI to recoup unpaid claims on bulk MI policies for stated income and other alternative documentation loans originated between February 2000 and the end of…