Bumping this thread up since I saw DJChris23 reporting an almost similar scenario in thread "Beware New bet Glitch that steals money" at Talk About Racing Rivals. I already received a reply 2 weeks after i reported my case. No compensation though.
Jabber, if its the difference on the weights of the cars that you stated, have you ever thought that it might be the CF Hood and Trunk installed on the lighter car? Also, try to read Shinbeats' guide which is stickied on the Tips Section.