The British Horseracing Authority has apologised "to everyone affected" after it was forced to overturn a result from Kempton on Friday evening.
Bird For Life was on the night announced the winner of a mile-and-a half handicap, in which 10/11 favourite was adjudged to have finished a nose away in second after a photo-finish.
However, after further viewing the result has been retrospectively changed and the placings reversed.
But the BHA said that "as per the Tattersalls rules of betting, the result that was called on the day stands for betting purposes".
Bookmakers Sky Bet have decided to retrospectively pay out on both winners as a gesture of goodwill. Racing PR Manager Michael Shinners said: "It’s a most unfortunate mistake and to be fair to those customers who backed the correct winner we have now paid out on both results."
You can watch a FREE replay of the race right here.
Brant Dunshea, director of integrity and raceday operations for the BHA, said: "Clearly the whole team is disappointed to have to correct any race result after the day. It is important that these results are called accurately.
"While it is appropriate that our processes allow us to put this right financially by the owner of the winning horse, we are aware that the betting public are significantly affected by issues such as this owing to the fact that the rules of betting mean that the result called on the day stands for betting purposes.
"We apologise to everyone affected."
Racing's ruling body has pledged to take action "to minimise the risk of a recurrence".
A statement issued by the BHA read: "The action, which is presently still being formulated, will provide further support for judges by ensuring that all photo-finish decisions are available for review by a BHA official before the 'weighed-in' is announced, ensuring that there is a second check before betting is settled.
The BHA added that, as a long-term goal, it has "already committed to improve accountability for decisions made on the racecourses".
