Gregg,
Years ago there used to be a rule on the books that called for a misdeal because two cards could not be dealt in tandem (succession) to the same player. This would occur if the first down card dealt to the button was exposed accidently by the dealer. This was a misdeal!
In the normal progression of a deal, this would have the dealer continue dealing and when he reached the button, he would deal the second card off the top, as usual, and then replace the exposed card with the very next card that would have been the burn if no mistake were made. This was NOT acceptable in the old rules, but now it is.
Somewhere along the evolution of new rules, this was changed and as far as I know is accepted. So...30 years ago we had a misdeal if the dealer exposed either the first or second card off the deck, or the first down card to the button. Today, exposing one of the first two cards off the deck still calls for a misdeal. However, the new rules allow the deal to continue if the first down card to the button is exposed. I hope I've explained it so you can understand the rule.