[l3]

Actually (assuming I have the mechanics correct) if the person is in stealth the game does test the other's spot and listen check. if either catches it we see the player. Which is basically, if a player hears a twig crack behind him or spots a shadow coming up next to his he will know another player is there but that player may or may not realize he's been made by his intended victim. It's the same in party if you cross a border in stealth sometimes your party members will suddenly be unable to see or hear you.