Brokerage ICAP PLC (IAP.LN) will not automatically cancel any Swiss franc trades that clients conducted after its EBS currency-trading system placed an accidental bid into the market Wednesday, a spokesman said Thursday.

"The deals are good deals, regardless of the trigger," he said, adding that it is up to clients whether they choose to write off any transactions.

EBS--the world's biggest bank-to-bank currencies trading system--rumbled the markets Wednesday by accidentally loading up a price for the euro against the Swiss franc that was 0.5% above the prevailing rate. The firm informed "all affected customers" of the error immediately after it occurred at around 1440 GMT, the spokesman said.

ICAP is conducting an investigation into what went wrong, and said Wednesday that "an incorrect price in [the euro against the Swiss franc] inadvertently entered the EBS live market due to a mapping error between the test- and production-trading environments."

The error caused some traders also to buy euros against the franc, as they saw the price spike as potentially the start of a larger move.

Most trading systems--including EBS--allow their users to cancel trades if both counterparties agree. It is a common procedure in the case of so-called "fat finger" errors that happen when users accidentally enter incorrect prices.

While such client errors are relatively common, a mistake such as this by a trading system itself is thought to be unprecedented.