But after broadcaster Sergeant quit the show following criticism from the judges, it was decided to continue voting one couple off each week until just two were left to compete in the final.
Now three couples will appear in next Saturday's final anyway.
The BBC's controller of entertainment production, Jon Beazley, called the situation "really unfortunate" but said: "There were exceptional circumstances at play.
Asked about viewers' complaints that producers should have anticipated the situation, he said: "They might be right.
"We have so many contingencies for a live programme of the complexity of Strictly Come Dancing, this was one extra set of circumstances we didn't have the contingencies in place for.
"Everything else, we could have legislated for. But that's the nature of the beast."
Earlier this year, the BBC was fined £400,000 by media watchdog Ofcom for misleading its audiences by "faking" phone-ins on TV and radio. A new code of practice was introduced after the furore.
Mr Beazley said the incident was "validation of the work that's been put into trust at the BBC".
Singer Stevens, dancing with Vincent Simone, and presenter Snowdon, partnered by Brendan Cole, had both been awarded 75 marks out of a possible 80 by the judges after their two dances, with Snowdon achieving a perfect score on her ballroom round.
That meant both couples were awarded three points to take into the audience vote, with Holby City star Chambers and partner Camilla Dallerup awarded just one.
In the audience vote, a further three would have been the most points Chambers and Dallerup could have won and a further one would have been the least either of the other couples could have got.
Therefore, whatever the outcome of the audience vote, Chambers and Dallerup would have been one of the two lowest-scoring couples and facing a dance-off for a place in the final against the other lowest scorers.
Lisa Snowdon achieved a perfect score in one dance
Speaking on BBC Breakfast on Monday, Arlene Phillips said she and her fellow judges had "no idea" there was a tie until Stevens and Snowdon's scores were announced.
"It's unfortunate the judges' scores combined to create the same amount," she said, explaining the judges enter their scores via keypads immediately after each dance's completion.
"It was a complete shock to us," she added, saying the judges "look at the leader board the same time as everyone else."
Phillips also stressed the judges will have no impact on which couple wins in next Saturday's final.
"We have no say next week - the public decide," she said. "Their votes will make a big difference."
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