An incorrect result was announced for the £75,000 EBF Final at Sandown, after the judge based his decision on a photo-finish taken at the wrong winning post.
This prompted outrage from bookmakers who paid out too quickly.
The 2m4f race, televised live on ITV4, finished at the second of two winning lines which Sandown uses for hurdles and chases, but judge, Paul Champion, was given a picture by the photo-finish operator taken at the first winning post and mistakenly called One For Rosie the winner by a neck.
After a lengthy delay, revised placings put Third Wind ahead, before the weighed-in signal, which is the official sign that bets can be settled.
However, some punters had already collected their winnings from on-course bookmakers, while all major off-course firms paid out on both horses.
A confidential report has been forwarded to the British Horseracing Authority (BHA) headquarters in London for further investigation – the blunder being attributed to human error by Racetech operatives.
This is the second time in a year that a wrong verdict has been called at Sandown, after Rio Ronaldo, was announced top in a 5f handicap on the separate sprint course, before Vibrant Chords was proclaimed victorious.
The judge lost his job over that mistake after an earlier blunder at Kempton in March, with the incidents prompting the BHA to review official handling of photo-finishes.
New protocols have been introduced involving a stipendiary steward verifying everything, before any announcements are made.
The fail-safe system usually works. It did not happen immediately, but it was sorted before the weighed-in.
Nigel Twiston-Davies, trainer of One For Rosie, said: “It is actually very depressing, even when mistakes happen.
Third Wind’s trainer Hughie Morrison said: “Nigel was extremely good and very philosophical. We had all accepted a dead-heat.
A professional punter came up to us in the winner’s enclosure and told us they’d got the winning post wrong.
“We didn’t know if we’d got up on the second line, but it looked to the naked eye like we did. It’s not the way you want to win a race, but the horse probably deserved it because he hated the ground throughout.”