Financial stocks were slouching again Tuesday even as the rest of the market treaded water in anticipation of the third-quarter earnings season kickoff. Thornburg Mortgage ( TMA) was one of the biggest sector losers, tumbling 9.3% after the mortgage lender added another $236 million to its loss estimate on asset sales to $1.099 billion. It now approximates having sold $22 billion in high-quality adjustable-rate-mortgage assets, which compares with the prior $20.4 billion estimate. The Santa Fe, N.M., company based the changes on newly received documentation for sales conducted by third party financing counterparties, as well as sales that occurred after Aug. 17 and a single $6 million impairment charge on a mortgage-backed security. Shares of Thornburg were down $1.25 to $12.21. That helped weigh on the NYSE Financial Sector Index, which lately lost some 22.7 points, or 0.2%, to 9,615.57. MarketAxess ( MKTX) also had a quick fall after the online broker's total September trading volume sank to $20.9 billion vs. $29.2 billion a year ago and $23.1 billion last month. Shares of the New York-based company shed 77 cents, or 4.9%, to $15.07. Meanwhile, Sallie Mae ( SLM) sued the J.C. Flowers-led group that last week revised its takeout bid for the student lender following the signing of a new law that will cut education-lending subsidies. Sallie is seeking $900 million in damages and an outright termination of the deal, as well as a declaration that the group "repudiated" the agreement and that no "material adverse effect" occurred.