According to the official service manual the deco should disengage over 350 rpm, released by the flythingy described by Arizoni.
Very often it doesn´t and sticks, with very different results as we could see. Sometimes the sprag clutch immerdiately disintegrates, sometimes the clatter phenomenon goes on for a long time without any damage. Surprisingly it starts very often between 3000 and 4000 kms, if you pay attention you can hear the same "click"-sound when powering down the motor, too.
Until now there isn´t a final sollution at hand, although it´s possible to get more stable sprag clutches. A deactivation, as Br. ES-335 (R2-D2?) describes, maybe is the only final answer although the starter would have a tougher life in this case and could aswell pass away early.
In case of Precious the clattering started at about 4000 kms, fortunately until now - 13000 kms - without a failure.