Hmm, well since the track temp. rose your overall traction should also rise. It seems either 1. your front traction increased at a greater rate than you rear traction and the front is over-dominating in the corners or 2. your rear tires are generating too much heat and they're fading. I suspect it's the former. If so, then maybe take some camber out of the front -> 1deg.
How were your tire temps.? You don't really need to measure them, but did they feel hot? Was it loose from the beginning of the race or did it develop over time?
Besides trying to answer the "why," I think the general advise would be to do the setup things necessary to make the car more pushy (or less oversteery).
Team Associated | Reedy | Airtronics
RC Excitement: Fitchburg, MA | RC Madness: Enfield, CT | Horsham RC