On Sept. 13, United States-based crypto exchange Kraken experienced a bug that allowed some users to buy or sell Bitcoin (BTC) at a notably different price from Bitcoin’s actual market price due to a reported system bug.

The next day, Kraken posted a Twitter thread explaining that the bug resulted from testing an unreleased advanced order type. While Bitcoin was trying to hold $10,300 mark on the day of the reported system glitch, the exchange wrote that “some clients bought from the tester at $8,000 and others sold at $12,000 without clearing the intervening liquidity” through the bug.

Bug on Kraken on Sept. 13. Source: Twitter

Kraken explained that the bug led to an execution on either side of the $8,000-$12,000 spread, while no liquidity was exhausted. The exchange stated that stop market orders were correctly filled at market price, and suggested that affected clients submit a support ticket.

A Kraken spokesperson subsequently told Cointelegraph that a total of around $100 was executed. The trade only happened once and could only be initiated by a specific user in the beta program. Traders who were not in the beta program passively benefited.

Kraken co-founder and CEO Jesse Powel said that the tested feature had already seen thousands of automated and human tests over several months, adding “you can’t find all the bugs all the time.” He wrote:

“Agree that matching at trade to the wrong side of the book is an exchange error. Everything that happened after that worked as expected. Trade printed, stops triggered, other orders matched just fine.”

At press time, Kraken is the 56th biggest crypto exchange by adjusted daily trading volume of $97.9 million, according to CoinMarketCap. On Sept. 14, an anonymous wallet sent 260 million Stellar (XLM) worth over $15 million to Kraken, as reported by tracking service Whale Alert.