Wall Street analysts are trying to figure out why Ginnie Mae securities have been prepaying faster than comparable Fannie Mae and Freddie Mac deals, but so far there is not a lot of consensus on what’s behind the shift. Ginnie Mae MBS prepayment speeds in July ran 4 percent to 5 percent faster than comparable Fannie and Freddie securities, a trend that began back in the fourth quarter of 2003 and is at odds with the historical pattern that Ginnie’s prepayments lag behind conventional MBS.