Yes, if you go over 50%(attacker) or 75%(defender), your alliance will lose war. You will get message with warning, if you activate vacation, your alliance will lose war.
So pls explain how this is possible - in our realm, an alliance declared war but after war has started, at the same day, they went above 50% (they had 53% something). We checked it and verified it several times, but war wasn't over and they didn't lose..how is it possible??