The Swiss franc is the latest currency to have gone bump in the night.
At the point where the week’s global trading got under way in Asia, the euro abruptly shot up one whole point from SFr1.1325 before immediately dropping back down. The dollar made a similar move.
The way the swoon happened, with a drop in one big hit from around 22:06 on Sunday, London time, followed by a slightly longer path back up, suggests that the move was the result of human error, rather than a computer programme somehow spitting out the wrong price.
A public holiday in Japan meant that markets were quiet and the shock absorption that would normally have come from wider flows did not appear.
It seems that “a badly executed [trade] triggered the move, which was exacerbated by the thinner-than-usual liquidity due to the Tokyo holiday,” said Lee Oliver at market intelligence firm InTouch FX.
The mini flash crash, which took the franc down only to levels seen in the previous week, is the latest in a series of late-night wobbles in the foreign exchange market.
In the opening days of January, the yen leapt higher with no obvious trigger for the move.
That was a flicker in comparison with an ugly flash crash in sterling in October 2015.
Investors are increasingly unnerved by such events, with some 40 per cent of those polled by JPMorgan saying poor liquidity was a concern for them, up from 29 per cent in the previous year.