Ok, Up elevator refers to nose up, which would be pulling back on the stick, full down or nose down would be pushing forward on the stick.

If inverted, you push forward on the stick to maintain level inverted flight. First you will notice that you must fly at a higher angle of attack to maintain level flight, our "semi symetrical" airfoils are designed to be more efficent right side up. Therefore, your stall speed inverted is higher, now throw in nose heavy, and too much elevator and the wing will no longer want to fly.

This is not a spitfire trait, although every spit I have flown has always been elevator sensitive, that long tail makes a great lever.

S1