The Turnbull government was scrambling on Friday afternoon to determine whether a loophole in its same-sex marriage survey would disenfranchise about 113,000 "silent electors".
They were also forced to work out whether 16- and 17-year-olds could accidentally be included in the survey, but ruled this out late on Friday.
The unprecedented $122 million optional poll, now the subject of a High Court challenge to proceed over the coming four weeks, has caused a number of headaches for the government and its agencies.
It relies on the Australian Electoral Commission sharing the electoral roll with the Australian Bureau of Statistics, which is legal. However, the law expressly forbids the divulgence of the addresses of silent electors.
Those typically include MPs (and Opposition Leader Bill Shorten is one), judges and victims of crime who do not want to appear on the roll for privacy reasons. The Parliamentary Library said there were 113,000 such voters as of 2016.
Acting Special Minister of State Mathias Cormann, who earlier in the week was confident ballot papers would be sent to silent electors, released a statement on Friday saying that this remained the government's intention.
"Our commitment is for all Australians on the electoral roll, including silent electors, to have the opportunity to have their say on whether or not the law should be changed to allow same-sex couples to marry," he said.
AEC spokesman Evan Ekin-Smyth said: "The AEC is working with the ABS regarding this issue. Relevant advice will be provided when available."
Meanwhile in the High Court, chief justice Susan Kiefel said the full court would hear an urgent challenge to the validity of the postal vote on September 5 and 6. The hearing is expected to take one-and-a-half days.
The court heard an injunction to stop the postal vote going ahead before the hearing was not required because the ABS has agreed not to take steps to conduct the poll before September 12.
Two challenges to the validity of the vote have been lodged - one headed by Tasmanian MP Andrew Wilkie and the other by national organisation Australian Marriage Equality.
At a directions hearing on Friday, the court heard there is a significant degree of overlap between the two cases.
The Australian Marriage Equality challenge is confined to two legal issues about the validity of the manner in which the government authorised the expenditure of money to conduct the vote.
The $122 million for the survey was not authorised by an Act of Parliament but was provided to the ABS by way of an advance from Senator Cormann, who is also the Finance Minister, under the Appropriation Act. An advance to the Finance Minister may be made if there is an "urgent need" for the funds and it was "unforeseen".
An issue in the case will be whether the expenditure was "unforeseen". A directions hearing will be heard on August 16, which is expected to narrow the issues.
The government was also seeking advice on Friday about whether a legal loophole in the postal survey would accidentally allow 16-year-olds to vote.
A direction given by the Treasurer Scott Morrison to the ABS declared that anyone who made "a valid application for enrolment" on the roll before August 24 would be eligible to participate in the survey. People aged 16 and 17 can make a "claim for enrolment" but are not able to vote in elections.
Senator Cormann late on Friday dismissed speculation the loophole would give 16-year-olds the vote. "The survey instruments will be sent to those who are on the roll; 16- and 17-year-olds are not on the roll," he said.
Also on Friday, the Equality Campaign officially launched its bid for a "yes" vote, and signed up former ALP national secretary Tim Gartrell as campaign director.
Executive director Tiernan Brady said the postal vote was a "terrible, terrible process" but "we have a duty to prepare", and encouraged potential voters to enrol and check their address details.
"There are only 12 days left for people to enrol to vote," he said
"This is specifically important for young people because we need them to enrol to vote so they can defend their friends if we have to have this vote."
- with Amy Remeikis