Context matters
OK there is a lot skipped over on the background here. In 1840, the treaty was signed between Maori chiefs and the British crown, creating a new nation. The articles of the treaty were as follows...
1. Maori surrender sovereignty to the crown
2. the Crown will ensure property rights of all NZ'ers will be respected
3. All maori and non maori are equal before the law
All fine and dandy until one judge in the 1980s said in an adjunct to a decision that the treaty was "akin to a partnership". Since then, all those with an axe to grind have claimed that NZ is not one nation, but 2, and that the 17% of Maori have formed a partnership with the 83% of non-Maori.
When settling treaty disputes between the crown and maori tribes (called iwi), natural resources that maori used to control but sold to the crown, are sometimes managed under a "co-governance arrangement", where maori have a proven historical connection and this has been examined and agreed with the crown.
Nowadays it is trendy to make "co-governance" arrangements within organisations that are not the crown and therefore not subject to the treaty, which is constitutionally troublesome. There is also a trend towards creating "principles of the treaty" which are defined adhoc by the courts and not by the government of NZ. (one wag noted that the treaty was quoted as "a living document" but once changes beneficial to maori had been made, it stopped becoming "living".)
A popular refrain over the last 40 years in NZ is that Maori did not surrender sovereignty under the treaty and therefore require separate systems of benefit to them (health, education, justice, etc) Interesting to note the tax system does not seem to be part of that split.
One minor political party has a bill being progressed through parliament that would seek to define once and for all what the articles of the treaty actually mean, so naturally those who enjoy priviledge from it's current interpretation are rather resistant to this, and have cowed the major political parties into siding with them. Polling shows popular support for the bill but machinations mean it will not progress further in this election cycle.
A refrain from the politician promoting this Bill (David Seymour, who is himself of maori ancestry), is twofold. He asks
"What is so unfair about equal rights for all?", and
"Can you name me a successful democracy country where political rights are different for different races?"
Also interesting to note, emigration from NZ to Australia is ramping up, and is noted as having a result of a drop in support for the political right. The political left are floating the idea of a "treaty overseer" (essentially a house of lords) who will have veto rights over laws passed by parliament. This will not end well.