UKIP's assembly leader "demeaned" a Labour AM when he superimposed her face onto a woman in a low-cut top in a YouTube clip, an investigation has found.
Gareth Bennett broke assembly rules by posting the video, according to leaked findings seen by BBC Wales.
The inquiry came about after an outcry over a previous decision that found the clip not to be sexist.
Mr Bennett's spokesman said the leak was "malicious".
Mr Bennett published the clip on YouTube in May last year attacking Joyce Watson for referring to UKIP AMs as "rabid dogs" in a debate the year before.
In the since deleted video, Mr Bennett made derogatory comments about the AM, saying Ms Watson used to run a pub but "you wouldn't guess that from looking at her".
The clip, made before Mr Bennett became UKIP assembly group leader, added: "She doesn't look like the life and soul of the party.
"I'm not sure I would fancy popping in for a quick one at the local if I saw her pulling pints at the bar."
The words were accompanied by an image of a barmaid in a low-cut top, with Ms Watson's face superimposed.
Ms Watson complained to Sir Roderick Evans, the standards commissioner for the assembly, but he decided it was not sexist.
Under pressure from Labour AMs and following fresh complaints, Sir Roderick decided to reopen the case but recused himself from it.
Douglas Bain, a former standards commissioner for the Northern Ireland Assembly, was brought in by the assembly as an acting standards commissioner to complete the work.
- found material in the video amounted to gratuitous personal abuse, and found the video to be demeaning of Ms Watson and women that were aware of it
- ruled that material in the video would discourage women from putting themselves forward for public office
- did not accept that Mr Bennett did not know the possible sexual connotation of the phrase "popping in for a quick one"
- found Mr Bennett breached the assembly's code of conduct and the anti-harassment dignity and respect policy.
Mr Bennett had issued a notice to the press apologising for, in the video, "falsely claiming" Ms Watson had wasted public money.
By David Deans, BBC Wales political reporter
Douglas Bain's view that parts of Mr Bennett's video amount to gratuitous personal abuse is notable for one key reason.
It is a stark reversal from the position taken by the standards commissioner, Sir Roderick Evans, who did not think it was sexist.
Last year Sir Roderick did not deem the video worthy of further investigation.
That changed after BBC current affairs programme Wales Live covered his decision, prompting fresh complaints from Labour AMs.
Mr Bennett could face sanction from his assembly colleagues, but the findings once published may be further material for critics of Sir Roderick's original decision.
Mr Bennett has argued that the video's barmaid imagery was intended to be satirical; denied the video made direct references to Ms Watson's personal appearance; and that it targeted the Labour AM because of her hostility to UKIP.
Mr Bain's findings are yet to be delivered to the assembly's standards committee, which could recommend to sanction Mr Bennett.
Powers include excluding the assembly member for a period of time without pay - a move that would have to be ratified by the whole assembly.
Mr Bennett can make his case to the committee, which he is a member of, and can potentially appeal any decision they take. It would be the second time that the UKIP assembly leader has faced a critical report by a standards commissioner in the last year.
The AM agreed to have his pay docked by £2,500 over assembly spending on a damp office that was never used.
Jenny Rathbone, Labour AM for Cardiff Central, said she was "pleased that the acting standards commissioner has realised that the video was sexist and inappropriate".
"It undermined the dignity of our colleague", she said.
She added that there "possibly" may be implications for Sir Roderick.
A spokesman for Mr Bennett said: "We do not comment on politically motivated malicious leaks.
"Such leaks simply undermine the integrity and credibility of the complaints process."
A spokesman for Mr Bain said: "It is vital that complaints made to the commissioner for standards are investigated in confidence, and the outcome of any investigations remain confidential until the standards of conduct committee has completed its consideration of the matter.
"In order to respect that confidentiality, the acting standards commissioner does not comment on any leaked documents."
Ms Watson declined to comment.