Just to clarify matters I think the destinction should be made between starter motor disengagement (momentary reverse voltage applied to starter motor from Fadec) and mechanical bendix disengagement (which should happen the instant this voltage is applied).

The jist of the problem seems to be that despite the application of reverse voltage the bendix failed to disengage.

The manufacturers have since modified the starter clutch with 2 engagement slots to apply a more axial force to the sliding sleeve to reduce the tendency for the clutch to stick.

Rob.