The British Horseracing Authority has apologised after the Chester stewards incorrectly revised the placings of a race at the track last Friday.
Infrastructure won the extended one-mile-three-furlong event, but the second Dark Red was deemed to have hampered Lunar Jet, who dead-heated for third with Vivid Diamond.
Lunar Jet was promoted to second, with Dark Red placed third and Vivid Diamond fourth, but the rules do not permit horses who have dead-heated to be split, unless there has been interference between them.
Lunar Jet and Vivid Diamond should both have been promoted to second with Dark Red fourth - an amendment announced by the BHA on Monday following an investigation.
A statement said: "The BHA understands the impact this will have had on a limited number of bets and that some disruption may have been caused to both off and on course operators and their customers, and apologises for this.
"It will now consider what steps to take in the future to minimise the risk of such an incident re-occurring, which may include publishing specific guidance relating to interference involving horses who have dead heated."
