Not all notaries would agree with you I'm afraid Dafluff. I've asked about this over the years because my wife's father is a quite successful businessman now in his eighties and I wouldn't want my wife to miss out on her right to inherit simply because I'm a WNA. Over the last couple of years I have asked no less than six notaries and the score is 3-3. Three agreed with you that inherited property could be inherited without a problem while the other three made the point that the law is applied differently depending on ethnicity and cultural traditions.
For a pribumi couple (native Indonesian) the law is indeed that the inherited property doesn't become a joint asset ('harta gono-gini or harta campur').
However, according to half of the notaries I put the question to, different rules apply to marriages between WNI and WNA. And I should add that the three that told me this did seem more knowledgeable.
http://irmadevita.com/2012/kewarganegaraan-status-pemilikan-tanah-warisan-pada-perkawinan-campuran/
Having said all that, the average official won't have a clue about this because they rarely encounter such a situation.
Then the 3 that disagree are wrong, yet I am surprised that the other 3 got it right. For those that disagree, simply ask them to produce a law that states mixed-marriage WNI lose their right to control their own assets brought into the marriage or inherited assets. There isn't one.
Even that article you linked repeats the same claptrap about pasal 21 ayat (3)) UU No. 5 Tahun 1960, and arrives at the wrong conclusion she confidently wrote in bold and italics. Here is the relevant pasal in full:
Pasal 21
(1) Hanya warga-negara Indonesia dapat mempunyai hak milik.
(2) Oleh Pemerintah ditetapkan badan-badan hukum yang dapat mempunyai hak milik dan syarat-syaratnya.
(3) Orang asing yang sesudah berlakunya Undang-undang ini memperoleh hak milik karena pewarisan tanpa wasiat atau percampuran harta karena perkawinan, demikian pula warga-negara Indonesia yang mempunyai hak milik dan setelah berlakunya Undang-undang ini kehilangan kewarga-negaraannya wajib melepaskan hak itu di dalam jangka waktu satu tahun sejak diperolehnya hak tersebut atau hilangnya kewarga-negaraan itu. Jika sesudah jangka waktu tersebut lampau hak milik itu dilepaskan, maka hak tersebut hapus karena hukum dan tanahnya jatuh pada Negara, dengan ketentuan bahwa hak-hak pihak lain yang membebaninya tetap berlangsung.
(4) Selama seseorang di samping kewarga-negaraan Indonesianya mempunyai kewarga-negaraan asing maka ia tidak dapat mempunyai tanah dengan hak milik dan baginya berlaku ketentuan dalam ayat (3) pasal ini.
Ayat 3 translated:
Foreigners who after this law becomes valid acquires hak milik due to inheritance or joining of property due to marriage, also WNI who owns hak milik and loses their citizenship, must relinquish that hak milik within 1 year of acquiring it....etc etc.
Ayat 4 translated:
When someone has another nationality besides WNI, then he/she can no longer own hak milik, and ayat 3 applies to them.
As you can plainly see, nothing about mixed marriage WNI. It only says foreigner, or WNI who lost their WNI status (in other words, again foreigner), or dual nationals, can not own Hak Milik.
The conclusion that a mixed marriage WNI can not purchase Hak Milik during the marriage is solely because according to Undang-undang Perkawinan (Marriage Law), UU no 1, 1974, assets purchased during the marriage becomes joint assets (unless a prenup was signed).
However, the very same law is clear that property owned prior to marriage, property gifted or inherited remain under individual control.
UU no 1, 1974
Pasal 35
(1) Harta benda yang diperoleh selama perkawinan menjadi harta bersama.
(2) Harta bawaan dari masing-masing suami dan isteri dan harta benda yang diperoleh masing masing sebagai hadiah atau warisan, adalah di bawah penguasaan masing-masing sepanjang para pihak tidak menentukan lain.
Pasal 36
(1) Mengenai harta bersama, suami atau isteri dapat bertindak atas persetujuan kedua belah pihak.
(2) Mengenai harta bawaan masing-masing, suami dan isteri mempunyai hak sepenuhnya untuk melakukan perbuatan hukum mengenai harta bendanya.
Translations:
Pasal 35
(1) Property acquired during marriage becomes joint property.
(2) Property brought into the marriage by husband or wife, and property acquired by them as gifts or inheritance, remain under their individual control, unless they agree otherwise.
Pasal 36
(1) In dealing with joint property, husband and wife must act with agreement of both sides.
(2) In dealing with property brought individually into the marriage, husband and wife have full right to act on their property.
I mean it is literally written black and white.