I was watching the bristol game and it was clear the scrum half was coming in front of the back foot to move the ball back with his foot.
So he is technically offside.
Howeve,r if you cantually whistled this, I am sure what would happen is they would go to the scrum half moving the ball back, then adding an extra man, moving the ball etc. and take even more time.
Perhaps we should prevent any player - from either side - joining a ruck once the ball is clearly won and the ref has called use it. The side that has won would have two seconds (five is an eternity) to use it or lose it.