According to the first naturalization act passed by Congress it was not necessary for both parents to be US citizens for a child to be a natural born citizen.
Obviously the view of who is a natural born citizen in 1790 was not an ironclad definition involving the necessity for two citizen parents at the time of birth.
BS
The act says "parents" - PLURAL
Furthermore the act did NOT declare those meeting the criteria (two citizen parents) to BE natural born Citizens. It declared that they are to be 'CONSIDERED AS' natural born Citizens. Basically, it says - we know they are not, but we will call them than any way. And the only reason that would be necessary is for the office of President. So apparently, some members of Congress wanted their offspring to be eligible for President even if they were born visiting family in the old country.
The fact that the passages was dropped 5 years later indicates Congress probably knew they screwed up and just quietly dropped it. But clearly - parentage was the prime driver in viewing citizenship rites. The act basically waived the jus soli requirement, incorrectly. So it was fixed by just removing it.
SR 511 makes the same mistake in that is says the act defines the definition of a natural born Citizen. But interestingly, if SR 511 did have teeth and was accurate Obama could not be eligible.
Under the requirement in the natuarlization act of 1790, the father still needs to be a citizen. This would still exclude Obama from being an NBC, of course.