Last week, WSJ stoked fears that the Feds might be ramping up another probe into abuse and manipulation in the foreign exchange market when it reported that Wells Fargo had abruptly terminated four bankers from its FX business and transferred another. Now, Wall Street’s paper of record is reporting that Federal prosecutors are investigating Wells for abuses in its FX shop – but the scope of the investigated is limited to one disputed trade.

According to WSJ, prosecutors have subpoenaed information from Wells and from the recently fired bankers as they investigate a trade and ensuing dispute between Wells and one of its clients, Restaurant Brands International Inc.

RBI owns several fast-food franchises, including Burger King, Tim Hortons and Popeyes Louisiana Kitchen. In an amusing twist, both companies count Warren Buffett’s Berkshire Hathaway as one of their largest shareholders.

In a statement, Wells Fargo said it “learned of an issue associated with a foreign exchange transaction for a single client. The matter was reviewed, the client was promptly notified regarding the issue, and Wells Fargo leadership took steps to hold accountable the individuals who were involved. Wells Fargo remains committed to our foreign exchange business, meeting our clients’ financial needs in an ethical way, and ensuring ongoing review of this and all business operations.”

The foreign-exchange issue revolves around a trade made within the past three years that included positions running into the billions of dollars, the people said. The trade resulted in a loss to Restaurant Brands, the people added, which led to a dispute between it and the bank. According to WSJ, pointed out that the investigation into Wells Fargo’s foreign-exchange business, which is housed within its investment bank, are separate from sales-practices issues that rocked the bank more than a year ago. Wells Fargo is planning to refund Restaurant Brands hundreds of thousands of dollars related to the trading loss, According to WSJ,’s sources said.The Federal Reserve is also looking into the issue. Specifically, Federal prosecutors are looking into the sequencing of the trade in question and whether it could have involved so-called front-running, some of the people familiar with the matter said. That should send a chill down the spine of the fired bankers, as earlier this week a US jury found a former HSBC currency trader guilty of fraud related to front-running a large trade that netted the bank some $8 million in profits. The US is also in the process of extraditing another UK-based FX trader to face front-running related charges in the US.