On any normal race day, champion jockey Douglas Whyte's record-equalling six wins would have been the most unusual event at Sha Tin but yesterday was no ordinary race day.

Whyte became only the second jockey to land six winners on a programme in the four decades of Hong Kong racing's professional history, matching Brett Prebble's six-timer at Happy Valley on June 20, 2010. In the process, Whyte took his own Jockey Challenge points record up to a new high of 94 points, as he also had three seconds and a third to go with the winners, and he stretched his championship lead over Zac Purton out to nine.

"It means a whole lot - it's one thing I've been missing. Numerous times I've had five winners and been unable to get that one more," Whyte said. "And it's very satisfying - I've had cards like this before, where you think you can ride four or five and you come home with a blank. You still have to deliver."

Deliver he did - in spades - as he wrapped his day in wins for John Moore in the first and last races, encasing three for John Size and a single for Peter Ng Bik-kuen.

But behind the scenes, the day was far from normal too, with Jockey Club stewards making a surprise sweep at the behest of chief steward Kim Kelly and blood testing more than 70 per cent of the runners in the final 10 races for bicarbonate levels.

There were 129 horses tested, from "a broad selection of all stables", with samples taken prior to horses being led to the saddling-up area.

"It's in line with our policy of ensuring a level playing field and part of the club's prohibited substance testing policy. We're seen as a world leader in the testing of prohibited and therapeutic substances, and this is in line with that," Kelly said. "Bicarb has been a substance of abuse in other racing jurisdictions, not so here, but we are just ensuring that everybody was within the threshold levels and we're very pleased with the outcome."

Reaction from trainers was overwhelmingly positive, tempered by some concerns about the pre-race timing.

And yet, even that "blue moon" event could not qualify as the day's most unusual - that belonged to the tierce betting in the ninth race. A tierce pool that might normally hold HK$7 million was holding HK$37 million, with HK$30 million of that on the 10-9-8 combination, which was showing a dividend of HK$11 for every HK$10 if it landed.

Officials said the bets were placed through several accounts but appeared to have been due to a software glitch at the punters' end, with the accounts placing the same bet over and over again.

"There is nothing suspicious about what happened, it was just a massive error," said chief executive Winfried Engelbrecht-Bresges. "The account holders are well-known to us as regular customers, but it appears they all used the same software and all had the same glitch."