Hi @Aleksandar Matejevic, 
Thanks for pointing this out. 

Yes there is a lot of weird things in the administrative boundaries mapping... 

For the official part : 
There has been different decrets (https://dev2lexpol.cloud.pf/LexpolAfficheTexte.php?texte=176935 and https://dev2lexpol.cloud.pf/LexpolAfficheTexte.php?texte=216633) about the creation of commune in French Polynesia. The subdivision (level 6) are to be a composition of admin 8 (commune) (see decret https://dev2lexpol.cloud.pf/LexpolAfficheTexte.php?texte=177598).  Commune have competences over the lagoon but it is not taken into account into the commune limites (it is confusing i think).
The official boundaries fit on the land as for now, and is shared on the local opendata sharing platform by the government and can be found here https://www.tefenua.data.gov.pf/datasets/3e956e20eec344bfb147682a38d7383e_0/  

Wiki page about administrative boundaries mapping : 
General OSM Community : https://wiki.openstreetmap.org/wiki/FR:Tag:boundary%3Dadministrative The local page wich is a bit more specific https://wiki.openstreetmap.org/wiki/FR:French_Polynesia/FR:French_Polynesia_tagging_guidelines#Limites_administratives 

Hope this helps, 
I will try to clean this,
Best regards,
Violaine