Yea it had dropped me down to 6th place already, no point in continuing. If you guys have some time, though, try this. Get the GT-R N24 Schulze, suspend the Tsukuba 9-hr Enduro, and see if when you resume the race, it does that. I went into the pits at like 100mph and as soon as the menu came up, I suspended it. Maybe that's why it glitched?
EDIT: I think I figured it out. The car, when I quit, was going too fast, so as soon as the pit menu comes up, it breaks out of pit lane, since it's on the strip before the walls. The game freaks out and keeps it in pit mode, I guess you could say, and drives the car by itself? It makes more sense in my head