The training switch kicks out and the EECs instantly respond by trying to restore Nr. They accelerate the engines against no resistance until they smash into the falling Nr. It is a very violent application of power and it's no surprise that this can result in transient Tq spikes
I'm puzzled by that statement, as the OEI training mode uses AEO (as you state), but displays OEI - unlike some types where an engine actually goes to idle and the other has an 'artificial' OEI limit but displays the real limits on the FLI etc. As the mode uses AEO, both engines are engaged and delivering a load (i.e. freewheels engaged), so isn't the real issue the fact that they will potentially go into 'blow away' power (or whatever AW/PWC call it), in an attempt to restore Nr, and use real limits?