At the pit stop exit where the rumbles strip is using the NSU cars: If you tire even touched the rumble strip the lap gets disqualified. I don't think this is not intended, since there is a 2 tires on track rule.
Hm i'll see if I get that too. Only on the short circuit? Edit: Yep, the rule on the short track is very strict. I'd say let us use the kerbs, but not go OVER the kerbs, because it still is an active pitlane.
I try not to hit the curbs, because it pulls my wheel hard if I do. If you barely nick it in places it will happen. It used to be this way on the others, but they were recently fixed.
Yeah, I found out that just kissing that inside kerb will invalidate your lap.. I don't often drive USA tracks though. I'm more of a Hungaroring guy.