some days ago I had just the same problem with one of Prblanco's tracks - I think it was Daytona Beach but unfortunately I must say I didn't find out what the problem was by the way - did you forget about the mod you said you would send to me...?
In Daytona's case, the problem is caused by the banked start/finish line. If I changed it to be flat, the problem disappeared. I tried messing around with the magic data but never found a solution.
Well, it's been a long time since I last touched it, but if I remember correctly the problem starts at quite low bankings, somewhere below 10 degrees. Also it seemed that the banking from the first two or three sectors caused it, after that it didn't matter.
great idea to finish Daytona - although the cars went around like snails and in the banked part of the track the tyres sank in it was great fun to drive resp. to imagine how it would be if it is completed... in other words, I love you track modders ))