Couple of things..............

Whenever you slam the throttle open on a model that's got little or no airspeed, you can expect the prop to do whatever it feels like doing. The airframe doesn't have the purchase to fight back. The airplane's stabilizing forces are in proportion to their airspeed. When the plane has enough airspeed the engine/prop will have minor effects when slammed WOT or jerked to idle. Turn that around, and the airplane turns around.

Also, when any surface is too sensitive the best solution all round is to reduce it's throws IN THE AIRPLANE.