Bank of America ( BAC) is apparently looking into trading "irregularities" stemming from at least one Merrill Lynch trader. The Charlotte, N.C.-based company, which closed its purchase of the brokerage firm on Jan. 1, is investigating trades made through Merrill's London office in the final months before the deal was completed, The New York Times reported. BofA is probing how Merrill accounted for trading losses, possibly by holding off on placing them on the books until bonuses were approved, the Times said. One London Merrill currency trader, Alexis Stenfors, in particular raised eyebrows at both U.K. regulators and BofA. The bank was so alarmed by the losses allegedly caused by the trader that it decided to investigate other trading positions coming from Merrill's London office. Stenfors apparently recorded a trading profit of $120 million for 2008 and was rewarded a large bonus, the article says. But three weeks ago, while he was on vacation, BofA discovered "irregularities" associated with his trading account. He appears to have lost a "substantial amount" on his trades, the Times says, citing a person briefed on the matter. The article states that Merrill executives also disagreed how to value certain trades of illiquid securities, specifically trades on an index of credit default swaps, which caused the losses to be delayed until after the bonuses were paid. Other issues within Merrill's trading businesses are also causing problems, the article states. Reuters reported that Merrill is working with authorities after discovering the trading irregularity.