Dozens of Coinbase users were complaining on Reddit regarding unexpected charges on their credit and debit cards; Worldpay and Visa issued a joint statement saying the issue was not cause by Coinbase; the Financial Times reports that the source of the problem was still not clear though it did seem related to merchant category codes that were assigned to Coinbase; the issues bring up concerns that regulators have been discussing, rules around the new digital currencies are not clear. Source.