Story updated to include comments from Oppenheimer analyst Chris Kotowski, statements from Goldman Sachs filing and Tuesday's stock price decline.NEW YORK ( TheStreet) -- Bank of America ( BAC) is well-known to mortgage-industry watchers as the most vulnerable of the big lenders to so-called "put-backs," but the market appears to be still catching on to the extent to which the bank distinguishes itself in this dubious category. Bank of America shares, which have underperformed big bank peers for months, took another hammering again on Tuesday, falling 1.69% to close at $12.23, their lowest close since Dec. 8, while most other big financials were higher on the day. "Everybody has this knee-jerk reaction that, when they're worried about housing, they're just going to sell all the banks, and that might have been appropriate two years ago when everybody had all the subprime paper, but if you look at the exposures now, BofA is in a class by itself," says Oppenheimer & Co. analyst Chris Kotowski. For those who need a refresher, put-backs -- or repurchases -- relate to mortgage loans that were pooled together and stuffed into bonds known as mortgage-backed securities (MBS) ahead of the financial crisis. The buyers of those MBS, mainly large institutional money managers such as insurance companies and pension funds, have in many instances lost a great deal of money on their investments. Many of them are taking issue with the way those MBS were put together, arguing that the mortgages that were put into those MBS were fraudulent or in some way did not meet the criteria originally promised. In November, when the issue of "put-back risk" was front and center in the media and with investors, shares not only of Bank of America but of other big and even medium-sized mortgage lenders were being battered daily due to the threat of untold billions in potential exposure. A widely followed report at the time from Compass Point Research and Trading, featured prominently in Barron's, put the total risk to banks at $134 billion. Since then, banks have spent a great deal of time walking investors through the risks of put-backs, and they are widely believed to have been overestimated. The latest scorecard comes from Nomura Securities, which in a research report on Monday drawn mostly from company financial filings, states that Bank of America is "in an unfortunate league of its own" when it comes to put-back claims.