But where does it end if an umpire looks at the big screen and changes his mind?
If an umpire walks up to Ponting or any other captain and tells him he's changing his decision, but doesn't say why, then it's understandable when that captain is exasperated by the decision (or both of them). Copping bad decisions is part of the game and he needs to accept that better than he does, however, a dangreous precedent is set when an umpire has a squizz at the big screen then calls a batsman back.
What happens if he gives a batsman not out, looks at the screen then sees he did hit the ball, does he then give him out? Do you call Martyn back 3 times in the '05 Ashes series when he plainly edged balls into his pads but was given out lbw? Where do you draw the line?
Either use technology or don't. The rule-makers cannot have it both ways. The umpires should not be operating in a vacuum. I went to the Supertest and got the proverbials with everything being referred, but the more I think about it, maybe the technology should be used. Tendulkar wasn't out and the decision would have been made by the 3rd umpire - no dissent from anyone and they just would have gotten on with the game.
There can only be confusion if the curent rules about only referring run outs and stumpings stay in, but umpires look up and change their minds about a catch or an lbw after seeing a big-screen replay. They must either not show the replays at the ground or use the third umpire to make decisions on all facets of the game. It may slow things down but they will get things right more often than not. That's especially important in the curent era where players are fighting for their careers as profesional players.
I'm not excusing Ponting's behaviour in this incident or generally, but I don't think you could say that his behaviour this time around was dissent. The umpire saw fit to approach him to explain his decision and initiated the conversation with Ponting, who responded to the umpire, who did not see fit to report him, nor did the match referee. There would be something wrong with Ponting were he not exasperated by an umpire changing his mind apparently by looking at a replay whilst on the ground. As Faap said, it's a unique situation and was probably dealt with as best it could be by all concerned.
The slow trudge off and the shake of the head by the disappointed batsman doesn't help the situation either - it gives everyone in the crowd watching, those at home and the umpires the suggestion that something was wrong with the decision - it's as much dissent as anything that is said by a player to an umpire.