It's a question of intent. Are they abroad temporarily or are they establishing foreign permanent residency?
That's what's interesting about the McClure case. Born in South Carolina to a father who later naturalized and moved the family out of the country with questionable intent to return (it was 1811, after all). At that time, naturalizing ex post facto naturalized minor children, too. However, overseas his naturalization either wasn't recognized or it was revoked leading up to the War of 1812.
-PJ
Understood. I was just thinking about how those factors mess up citizenship charts! All sorts of footnotes, exceptions, etc.