Fannie Mae and Freddie Mac single-family business slowed in February as the purchase-mortgage sector faltered, and trends suggest the GSEs are losing share in their core market. The two enterprises issued $50.05 billion of single-family mortgage-backed securities last month, according to a new ranking and analysis by Inside The GSEs. That was down 11.5 percent from January and left Fannie and Freddie production for the first two months of 2015 12.2 percent behind the pace set last year. February’s new issuance was also the lowest monthly total for the GSEs since May 2014, when they produced $44.80 billion of single-family MBS. Purchase-mortgage volume followed seasonal patterns and sank 18.5 percent from...