first you need to be in a 2 player party and go to Snowy Mountain Mission map, when i complete the F1 or F2 (any dificulty) mission map, here is the problem :
1. if i am not the leader, after completed the mission map, there is no any option or button to click for me to leave the map!
2. if i am the leader, there is a message pop out asking " Would you like to retry the mission at a different difficulty?" you can Confirm(F1) or Quit(F2). now i chose F1- confirm, then a message will pop out to let me chose the F1 or F2 map to play BUT i change my mind and no want to play any map, then i chose cancel at this time, the message will disappear, and now i am STUCK in this area with NO any option to LEAVE this place. after few second, the other party will "Automatic" leave the map. but NOT the LEADER!
the only way to get out of the map is to log out and log in again.