The strangest thing is that it'll only happen when a certain amount of cars are on screen. After the 40s mark, you'll see the the heads go amiss only until the last cars start to disappear into the corner (maybe only 20 helmets for the last cars will render?), hence my suggestion about the "limit some things'" option which unfortunately didn't work.
I've noticed before if you start a single car replay in the F3 view the head will be missing but if you press F1 and then back to F3 it'll reappear but that doesn't seem to work with lots of cars. Just have to hope Ilja can work his magic on it some time, Shader Patch brings so many goodies that a few glitches are inevitable I guess.