This has been a problem for quite a while and I'm sorry if this was brought up a while a go and dismissed.
When a lobby leader starts a 6s or Highlander match on a 5CP map and selects the UGC config it is automatically set in the server for a win difference of 5 instead of first to 5 as the UGC config should do.
I'd like it if this bug was fixed. This may seem like a small issue but there are instances where players will leave a game once one team reaches 5 wins as they believe the game is over when it's really not. Most people in NA don't want to play a match the full 30 minutes if the match is 5-2 in say 15 minutes.