Hello Arturia,
This appears to be a bug/regression in Prophet V3:
1.) Sustain Pedal (CC 64) used to be assigned to the "Keyboard Hold" (infinite sustain) on previous versions of Prophet. It is now assigned to the "Release" button. This exhibits different behavior.
2.) When using midi assign to try to re-assign the two buttons above (ie. unassign "Release", re-assign "Hold" to CC 64), Midi Control Setup ignores CC §4 events.
Thanks, Regards,
Kevin L