We were strictly obeying the course boundaries, and had a terrible time getting through narrow gates where DARPA's waypoint file had a narrow width designed to guide us through the gates. If you look at videos of our runs, you can see the vehicle backing up and trying to get through a narrow obstacle. It's trying to get past a real-world obstacle on one side and a GPS limit on the other, which has narrowed the allowed path to where it can't quite fit.
So for the second run, I put in a patch to add 1 meter to DARPA's lane width. But I forgot to push it out to the vehicle, and we botched the second test run. It was in place for the third test run, though.
My friend owns a Model S and on the way to lunch it got confused on off ramps and parts of the road that were not well defined by lines. It basically shut off autopilot and required my friend to take the wheel.
In the 2004 Grand Challenge, the bounds were much wider and most vehicles screwed up. As it turned out, you could almost drive the 2005 Grand Challenge by staying centered in the DARPA-defined path. But we didn't know that in advance.