First quarter data on thrift holdings of mortgage-related securities tell conflicting stories, with one report suggesting a modest increase and another pointing toward a small decline. According to the Office of Thrift Supervision, OTS-regulated lenders held $159.23 billion of mortgage securities on their books at the end of the first quarter. That was up 1.8 percent from the previous period and represented the industry’s highest investment in MBS in nearly four years. …