Very minor point, but what the heck - it's summer

[JC]

IMHO, it's a violation by any interpretation of the rules. The case where the touching is simultaneous as you describe (i.e. the 2nd hand touches the ball before it is released by the 1st hand) is an easy violation call. NF 4.15.4c "The dribble ends when the dribbler simultaneously touches the ball with both hands."

It is even a violation if the 2nd hand touches the ball AFTER it is released by the 1st hand (not simultaneous), but before the ball touches the floor. NF 4.15.2 "during a dribble the ball may be batted into the air provided it is permitted to strike the floor before the ball is touched again with the hand(s)."