Let's start a new thread on loss of speed turning downwind if anyone is interested! Basically, same effect as windshear. Aircraft have inertia (which is referenced to the earth and not the airmass in which an aircraft flies) and so IAS will not change instantly when the headwind component changes. You don't notice it too much in a 1000 kg aeroplane, but when you get to 250+tonnes.....
As for spinning, if you only teach someone incipient spinning and he tries it on his own and the aircraft does not recover, would it not have been a good idea to show him how to get out of a fully developed spin? A little knowledge is a dangerous thing!