2017 Law 20.10 Ending the scrum
(c) Hindmost player unbinds. The hindmost player in a scrum is the player whose feet are
nearest the team’s own goal line. If the hindmost player unbinds from the scrum with the
ball at that player’s feet and picks up the ball , the scrum ends.
2018 Law 19 Ending a scrum
b. When the ball reaches the feet of the hindmost player and it is picked up by that
player or is played by that team’s scrum-half.
More subtle wording changes '17 to '18.
I know it must be there but I can't find any reference that requires players to remain bound until the scrum ends or, 2018 Laws, prohibits the hindmost player from picking up the ball prior to unbinding.
Clearly the scrum hasn't ended until the ball is picked up but where is the violation of law for the #8 binding only with hands?