How useful are stock ratings? A glitch at Citigroup spanning more than four years has given investors another reason to ask that question.

The bank’s electronic feed distributed inaccurate analyst ratings to individual retail customers, sometimes giving a stock a “buy” rating instead of a “sell,” or grading a security that it didn’t actually cover, according to the Financial Industry Regulatory Authority (Finra).

The error affected more than 1,800 securities, though its research reports, which were available to brokers, had the correct ratings. Some customer portfolios that weren’t supposed to contain stocks with “sell” ratings included them anyway because of the glitch, and its online portals for clients displayed inaccuracies. Finra slapped Citigroup—which neither admitted nor denied the charges and had self-reported the issues to the regulator—with an $11.5-million fine.

It isn’t clear from Finra’s statement how much money, if any, Citigroup’s customers lost because of the technology problem. In this instance, it would actually be worse if customers didn’t lose anything from the mixup. That would demonstrate that its analyst ratings aren’t useful. Citigroup may be in the peculiar position of having to assure clients that they lost some money—but not too much: As part of the fine, Citigroup has to pay at least $6 million in compensation to retail customers.

Analyst ratings on stocks have been contentious in the past. Regulators say former Citigroup (Salomon Smith Barney at the time) analyst Jack Grubman issued misleading and fraudulent research reports to help his employer secure investment banking business. Grubman was barred from working in the securities industry for life.

Other brokerages had similar scandals (paywall), which led to a separation of research and investment banking functions across Wall Street. While the reforms were implemented years ago, analysts have told Quartz that they still feel pressured to provide positive “buy” ratings on the stocks they cover or risk losing out on business from those companies down the road.

Citigroup’s recent glitch appears to be of a different nature—an inadvertent technology error. Even so, if analyst ratings are important, how did the errors persist for so long? While apparently just a systems malfunction, it raises much bigger questions about the value and role of stock ratings in modern financial markets.