I'm flying a Goldberg Skylane 62. Semi-semetrical high wing, small amount of dihedral. When I do a roll, the roll rate nearly doubles when the plane is inverted as soon as I add down elevator to maintain altitude. I'm fairly certain that it's the application of down that causes the rate to go up. I'm not using any rudder during the roll because the coupling effect is too strong. Anybody know why this happens?