"In this case, Law 11.3(c) should have been applied, putting Welsh onside. The appropriate decision, therefore, should have been a scrum to Australia for the original knock-on."
Joubert has been widely criticised for his role in Scotland's World Cup demise but received support from World Rugby High Performance Match Official Manager Joel Jutge.
"Despite this experience, Craig has been and remains a world-class referee and an important member of our team," Jutge said.
All match official performances are thoroughly reviewed and assessed by the World Rugby Match Official Selection Committee comprising John Jeffrey (Chairman), Lyndon Bray (SANZAR), Andrew Cole (SANZAR), Donal Courtney (EPCR), Clayton Thomas (Six Nations) and Jutge.
Appointments for this weekend's semi-finals will be announced in due course.
Meanwhile both Australian coach Michael Cheika and World Rugby boss Brett Gosper believe Joubert's running off the field was not an admission of error.
Cheika sympathised with Joubert - an official with whom he's had robust disagreements in the past - saying the hostile atmosphere which filled Twickenham, with boos and bottles being hurled onto the field, would have played a part in the referee's quick exit.
"Someone threw a bottle at him, didn't he? I don't think that's funny," Cheika said on Monday.
"If I saw a bottle being thrown at me, I'd be getting off (the field) as well. Maybe he was worried about something?
"Maybe he got a word in his ear from the security guards of the tournament organisers to say 'We think you should leave the field' because who knows?"
Gosper used humour to play down the seriousness of the situation, but described Joubert as a "superb referee and a good man".
He also confirmed there would be a review of the refereeing performance, as is standard practice.
"Maybe he was keen to get to the bathroom, who knows?" Gosper told BBC radio.
"I'm sure as a referee he sensed a bit of hostility.
"When you have a hostile 82,000 people, for whatever reason, who knows how that affects behaviour."
In defending Joubert, Cheika referenced a recent disagreement with the South African official who had sin-binned Waratahs flanker Jacques Potgieter and awarded a penalty try to the Highlanders in a Super Rugby semi-final this year.
Potgieter had come in with a swinging arm and connected with the head of Highlanders' Lima Sopoaga, who was in the act of scoring a try and was quite low to the ground.
The decision was crucial, with the match poised at 20-17 at the time, and the Highlanders went on to triumph 35-17.
But, while initially upset at the call and the end of his team's season, Cheika soon saw reason.
"He backed it up clearly in the very methodical way that he makes his decisions," he said.
"As frustrated as I was, you've just got to wear that. And probably at that point it cost us big time in the game.
"I don't like (what) people are making out of the way he ran off the field.
"You've got to assess things for what they are. He is just a human being like you and I are."
-AAP