With all the misguided fuss the DPP made about his expired US Green Card a few years ago, I wonder why this hasn't been brought up yet.
According to the Basic Law of Hong Kong, "Chinese citizens born in Hong Kong before or after the establishment of the Hong Kong Special Administrative Region" are Hong Kong permanent residents and have the right of abode in Hong Kong. Unlike US permanent residency, the right of abode is held for life (...or at least until 2047) by Chinese citizens born in Hong Kong, and does not expire due to extended absences from Hong Kong.http://www.gov.hk/en/residents/immigrat ... /eligible/
All President Ma needs to do is to go to Hong Kong, submit his birth certificate and form ROP145 to the Immigration Department, and he will be entitled to a Hong Kong permanent identity card and HKSAR passport. After this, he cannot be denied entry to Hong Kong, or be deported from Hong Kong, and can vote and stand in Hong Kong elections.
Before the handover in 1997, Ma's status was that of the British Dependent Territories Citizen under the British Nationality Act 1981; his British nationality was automatically lost due to the handover. By being born in Hong Kong, he was a Citizen of the United Kingdom and Colonies with Hong Kong belonger status from birth and until 1983, and a BDTC with the right of abode in Hong Kong from 1983 until 1997.
One of his daughters - the one without the US passport - also qualifies for the HK permanent identity card, HKSAR passport, and Home Return Permit. The one born in America probably doesn't; since her parents had US Green Cards at the time of her birth, she is not considered a Chinese national. But since British Nationality Law permits dual nationality, she was also a BDTC with the right of abode before the handover in 1997, so as a former permanent resident, she hold the right to land in Hong Kong. The right to land is like the right of abode, with the main difference being that she would be able to vote or stand in elections, and could be deported as part of a conviction for a serious crime.