A costly difference of interpretation between the Mortgage Guaranty Insurance Corp. and Freddie Mac over a pool insurance dispute has prompted the mortgage insurer to file suit against the government-sponsored enterprise and its regulator, the Federal Housing Finance Agency. Filed earlier this month in the U.S. District Court of Milwaukee, where the company is based, the legal dispute concerns differing readings of the “aggregate loss limit” for insurance policies MGIC provides on 11 pools of Freddie loans. The aggregate loss limit is about $535 million higher under Freddie’s...