In simple terms:
After activating OP CLB, if you dial back (or manage down) the speed for zoom climb BEFORE N1 would spool to +95 N1, the A/THR is still active and will follow the slower target by reducing thrust.
Ce n'est pas un bug mais une fonctionnalité.
More regrettably, this is another thread hijacked by the Airbus borg brigade.
In my defence, I have no choice.