Actually the fuel tank on most racers are bladder tanks on the CG to prevent CG changes from full to empty. You will find racing airplanes are very accurately balanced for lateral and sometimes aft cg to allow for the right characteristics in closed course high speed flight.

This event occurs on race planes that are trimmed at high speed, often set with a slight noze down (for knife edge control of pitch, and another topic). This appears to occur on shoulder wing as well as low to mid wing planes, seems to be airfoil dependent. The original Neme Q with a laminar and reflex airfoil (I think thats what they called it, refering to the trailing edge profile).

wkevinm