Maybe Mark thought Maintain the gap meant pass him and get 3 seconds ahead of him? 
Well, Sebastian was in 2nd position in Malaysia. Maybe he thought multi 21 meant "driver now in 2nd position must take 1st"

That clip just shows Mark putting the Red Bull's balls by Vettel's face and then backing off, showing he was faster than Vettel that day.
Mark was very clear about his actions:
“I ignored the team and I was battling to the end.”In 2012, he again was very clear that he has no intent on obeying teamorders.
Both from Webber's standpoint (being screwed over by your team-mate), as from Red Bull's (having a driver disobey teamorders), Vettel's actions were not unique. Even the now debunked myth that it was not a fair fight because Webber's car was turned down was a bust anyway, as Mark disobeyed teamorders while Vettel's car was actually at a disadvantage, as its KERS was bust.
As he often is when the car isn't perfect.
Leaving aside the 'often' discussion, Webber was faster at the end of that day because 1) Vettel had a screwed-up pitstop and 2) Vettel didn't have KERS.
You can have your digs at Vettel's skills, but don't try to misrepresent the facts of that day.