Rats, I was hoping it was just 1 track, there are a few tracks out there with issues resulting in your problem.
I'm out of ideas now, no idea why the cars are set back in lap. it should not happen at all.
Last resort: install rfLite in another directory, just for a test. install the mod and try and replicate the issue again. you might get lucky here if the problem doesn't return, then you know you will have to either start using rflite or re-install the current rf install.