Ken,
Substantial action is irrelevant once the player looks at his three cards. The SB hand is dead, and play continues. You might want to consider returning the player's SB amount. We actually had a "slush fund" for such occurrences, based on the dealer (or house) mistake. After killing the SB, I would take one of the dead cards (face down, of course) and return it to the deck as the burn, thus assuring proper card for the remainder of the hand. Players need to protect their own hand. If the extra card were noticed before it was picked up and mingled with the proper cards, it could have been returned to the deck, no problem. Unfortunately, that did not happen.
That's how I see it.