I myself along with some friends run a league, there arent many of GT5's oddities that we havent got our heads around now, the issue your talking about can mess races up but is easily fixed, set your room up then start a race, get the guys who entered the race to quit out, from then on that room should adhere to the 'fastest first' setting whenever you qualify before another race, if you open a different room then you have to do this again. The only other time you have to do this once the room is open is when you change the course to a weather/time change track.
When you open a new room sometimes this bug doesnt happen, but often it does, so when we are racing a league event its worth doing this preliminary quited race start before you start qualifing (I also write down quali times so if it still happens we simply line up on track in order and re-start ). I hope this helps.
