Melbourne stewards have suffered through a second blunder concerning jockeys riding with the incorrect weight, this time at Wednesday's Sandown meeting.

Only hours after dealing with a debacle that arose at last Friday's Ballarat meeting, stewards discovered apprentice Damien Thornton had been allowed to ride with 1kg less than he was entitled to in two races at Sandown.

The confusion arose after Thornton's 3kg claim was reduced to 2kg after he rode his 20th city winner at Moonee Valley last Friday night.

But racing records were apparently not updated and the official list used by the clerk of scales on Wednesday still showed Thornton claiming 3kg, as did the racebook.

He therefore weighed out 1kg light in the first two of his three rides for the day.

Thornton said he had experienced a "mental blank" concerning his claim, but became aware of his error before he was due to ride in a later race and immediately told the stewards.

The two horses he rode light were disqualified, he was reprimanded and the stewards made a report to Racing Victoria's Integrity Services department.

Earlier on Wednesday, stewards had delivered a reprimand to Jackie Berriman who had claimed her 3kg allowance in a race at Ballarat in which claims were not permitted.

Berriman's horse duly won and was subsequently disqualified after correct weight was declared and winning bets paid.

The stewards admitted their mistake in the Berriman case and a report has been lodged with Integrity Services.