If you're getting into a spin just by kicking full rudder at the top of a vertical maneuver, something is wrong with what you are doing. Kicking full rudders shouldn't put into you into an accelerated stall situation. However, pulling back on the stick all the way into your guts will get you into an accelerated stall and if that is the time you decide to use any rudder input, no matter how minor will most likely throw you into a spin.
Which goes to show that you have to make the P-38 spin, it is pretty hard to get it to do it itself.
ack-ack