The Church of England's governing body is facing embarrassment as it emerges members voted by accident against a report keeping the Church's conservative line on marriage.
The shock result on Wednesday night saw the key report by bishops thrown out by clergy members.
But synod members have now confessed they pressed the wrong button on the General Synod's electronic voting system.
The revelations raise concerns over the result with a majority voting to pass the report but a technical procedure meaning it was defeated by just seven votes. If only four members of the House of Clergy made a mistake the motion would have passed.
One lay synod member, who accidentally voted against the report, told Christian Today of the chaos in the chamber, saying a lot of people were unsure what they were voting for.
'Other people around me were talking about their own misunderstandings,' he said.
'The voting wasn't clear. I have concerns, someone got shouted over, it was very confusing.'
He added: 'It was more of a colluding with people rather than an orderly debate.'
It comes after the Bishop of Coventry, Christopher Cocksworth, was forced to apologise to the Archbishop of Canterbury for also accidentally voting against the report.
'Much to my embarrassment,' he wrote in a blog post, 'I have managed to give the impression that there was not complete agreement in the House of Bishops that the Report provided us with the best way forward.
'Due to a moment of distraction and some confusion over the voting process, I pressed the wrong button on my handset, thus registering a vote against taking note rather than a vote for taking note of the Report!
'I have apologised to my colleagues in the House of Bishops and to the Archbishops for my mistake.'
Most synod members voted to pass the report but a move by campaigners forced the synod to split into its three houses – the laity, clergy and the bishops.
The bishops and laity both passed the report but it was voted down by the clergy with a majority needed in all three houses.
Because of the technicality if just four clergy members made the same voting mistake the result would be down to an error.
But a Church spokesman said he was not aware of any clergy voting by mistake.
'We are aware that the Bishop of Coventry and a member of the House of Laity have reported pressing the wrong button in the vote following the take note debate on the House of Bishops' Report on marriage and Same-Sex Relationships.
'As the results in both the House of Bishops and House of Laity were strongly in favour of the report there is no material difference to the outcome of the vote.
'It is the responsibility of Synod members to follow debates and the business of Synod carefully and to cast their votes accordingly.'
He added the questions over incorrect voting would not lead to a recount.
'There are no procedures under the Standing Orders to withdraw or change a vote on a Synod motion once cast,' he said.