We just ran into two situations of culture clash in our group.
In the first incident, gamers with a wargame background played against gamers with a Eurogame background. A deal was made during the game between player A (Eurogamer) and player B (wargamer), and unilaterally broken on the last round of the game by player B, after all of player A's actions were over. This was our first playing of anything resembling a wargame (Wallenstein).
The treachery was a complete surprise to the Eurogamer. He had left his postion completely open to player B, because he had assumed that a deal made is as binding as any rules of the game in print, unless given advanced notice of intent. Player B assumed that deals were to be made and broken when to the advantage of the one who wants to break it. Who was right?
The answer is that neither one was right or wrong. Both styles of play can be acceptable, as long as prior understanding is given before cracking the game open. It is the gaming group that must determine if deals in any game not specifying must be kept or only held under a balance of power. At the very least it is the group who play the game that must agree to it, before the game is started.
I like to think of it as players and characters. The players are the people that come to play, the characters are the personas they take up when they play. The players must decide what rules the characters must abide. Once done, it is up to the characters to decide what to do within the game rules.
Only note: the answer that "the lesson was learned for future games" is not acceptable to me, because it implies that player B "knew" a rule of the game that player A did not, and exploited this, which is patently unfair.
The second clash involved the classic question of what to do on your last turn when you can't win. Player C, a wargamer, decided to inflict a loss on player D who had attacked him (in a normal game play) earlier in the game. This one is much harder to answer, because it depends on why he did it. (We were playing Taj Mahal)
If he did it because it was really the best move for him to maximize his position, it seems "right". If it was done because he wanted to "remain in character", it could also be "right". On the other hand, if he did it in order to dissuade player D from attacking him in future games, it seems "wrong". I think some combination of the second and third was closest to the truth, but most unconsiously; it is just what wargamers do. They attack people who attacked them. This was another surprise to the Eurogamers.
My hesitation is that among wargamers, I believe that there are some who play with a kind of quasi-roleplaying which extends toward any game. They think that it is normal and correct to "get back" at an offending player during the game, even if it does not maximize their points, and would maintain that it has nothing to do with metagaming issues.
I don't want to be in a position of telling a player that they need to choose or to not choose a certain decision in a game. I hope that they will not choose actions that offend people outside the game board if they are playing with non-wargamers. I also hope that other players do not take offense when another player makes a reasonable move against them. That is why the first attribute of a gamer must be good manners.