Jumbo mortgage securitization increased slightly in the third quarter, thanks to surging volume in the subprime and Alternative A MBS markets, a new Inside MBS & ABS analysis reveals. A total of $82.91 billion of loans exceeding the Fannie/Freddie conforming loan limit were securitized in the non-agency MBS market during the third quarter. That was up 7.2 percent from the previous quarter and brought year-to-date issuance to $209.28 billion – a gain of 1.2 percent…