I hosted a 6v6 lobby earlier today and in the middle of the game, the lobby closed with this message "Lobby closed: MATCH_ENDED". The score was 2 - 2 and we were still in the middle of the 5th round, so the match was definitely not over.
In the match stats, it looks like the stats of our lobby were merged with a Highlander match. Our sixes lobby was on servechi5.tragicservers.com:27015 and the lobby number was 260508.