The organiser of UKIP's assembly leadership election has apologised to candidates after about 300 new members were unexpectedly given a vote.
Caroline Jones, Neil Hamilton and Gareth Bennett were originally told members had to be in the party for six months before they could take part.
But after UKIP took legal advice they can now vote after being in the party for just 28 days.
Piers Wauchope, the party's returning officer, said he had "egg on his face".
"I'm very embarrassed, to have set off on one tack, to be told I couldn't do it," he said.
BBC Wales spoke to Mr Wauchope after concerns were raised privately of reports of recently signed-up UKIP members receiving ballot papers.
Some party activists were worried the additional ballots may give Neil Hamilton an advantage.
But Mr Wauchope said he could not see "any way it can be rigged for one person or another".
The number of people eligible in Wales to take part in the ballot now stands at just short of 900, according to Mr Wauchope , after around 300 new members joined in the last six months.
"We have a conflict between the party constitution and the rule book and that's really what it is," he said.
"I had hoped to run it by the rule book which would have entered a six-month rule.
"Sadly the constitution gives everyone who is a member in good standing has the right to vote after 28 days."
Mr Wauchope said he had taken legal advice and been told "the rule in the rule book is a nonsense because it tries to overrule the constitution which it's not entitled to do".
UKIP has claimed its membership rose after individuals on the radical-right known for their presence on social media joined the party.
It also claimed that Theresa May's Chequers agreement on the UK's Brexit strategy helped recruitment.
Some members speculated that those who joined in response to the social-media personalities' recruitment may be inclined to vote for Neil Hamilton.
He had enthusiastically backed the recruitment of the activists himself in a Twitter post earlier this year.
A source close to Gareth Bennett had no concerns, saying the candidate was "perfectly comfortable with members having their say".
Neil Hamilton and Caroline Jones were also approached for comment.
The vote has already suffered a delay, said to be due to a problem with the printing of ballot papers.
It was originally meant to have been done by the end of July, but the count is now expected to be completed on 10 August.
Members can pick their first and second preference candidate under the supplementary vote system.
The ballot was called by UKIP following the ousting of Neil Hamilton from the job of assembly group leader by Caroline Jones, after two other AMs backed her.
Recently the group of five in the assembly has been dogged by a row over the appointment of an assembly commissioner.