I was watching Poker After Dark 2011, the cash game Pot Limit Omaha weeks. And it looks like once in a while the winner only shows the two cards making the best hand and not the two other cards.
Is there a rule specifying that the winner as to show his four cards or specifying that showing two cards is sufficient?
Note that I'm not talking about the (official but very bad poker etiquette) rule where someone can ask to see the hand of a player who folded and hence lost the deal.
Here I'm specifically asking about the winner's hand.
On most online poker rooms the winner's entire hand (i.e. the four cards) is written in the hand history (and the hand of everyone who went to showdown too, but that is another topic).
But what about live Omaha? How does it typically work in Omaha cash game and Omaha tournaments?
If there's no official rule, what typically happens?