Maori Sovereignty and the Treaty of Waitangi

Recently there have been a number of announcements that Maori did not cede sovereignty when signing the Treaty of Waitangi with the Waitangi Tribunal concluding,

The rangatira who signed te Tiriti o Waitangi in February 1840 did not cede sovereignty to the British Crown
Waitangi Tribunal

This is obviously a huge problem, although not in the way most people think or most media outlets are reporting on. In fact, it may be a giant own goal by the Waitangi Tribunal.

The fact of the matter is that the Crown acknowledged Maori as sovereign. In the words of Lord Normandy,

I have already stated that we acknowledge New Zealand as a sovereign and independent state so far at least as is possible to make that acknowledgement in favour of a people composed of numerous dispersed and petty tribes, who possess few political relations to each other, and are incompetent to act or even deliberate in concert. 
Lord Normandy's brief

Lord Normandy's brief is actually an amazing document and should be read by any having suspicions of the motives of the Crown. That only a decade after the outlawing of slavery in the British Empire the Crown is willing to treat with Maori in a reasonable manner is incredibly progressive.

The brief also contains the Crown's motives and expectations in regards to New Zealand.

Her Majesty's Government have resolved to authorise you to treat with the aborigines of New Zealand in the recognition of Her Majesty's sovereign authority over the whole or any part of those Islands which they may be willing to place under Her Majesty's dominion.
Lord Normandy's brief

There is a clear expectation that Maori cede sovereignty. This expectation is repeated over and over again throughout the records of the time. Hobson's instructions were very clear and it was his belief that he had fulfilled them, or perhaps a better way of stating it is that he presented the outcomes of his actions as having fulfilled his instructions. 

Which is where I think the mistake has been made. If the Crown did not gain sovereignty over New Zealand while in the belief that it did gain sovereignty over New Zealand then it allows the Treaty to be invalidated.

A State may invoke an error in a treaty as invalidating its consent to be bound by the treaty if the error relates to a fact or situation which was assumed by that State to exist at the time when the treaty was concluded and formed an essential basis of its consent to be bound by the treaty.
Article 48 - Vienna Convention on the Law of Treaties (pdf)

We are a signatory and have ratified the Vienna Convention on Treaties. It would need to be run past a fleet of lawyers (I am not one) but it would seem to me that if this is valid then the Treaty of Waitangi is no longer a viable path to reconciliation as this can be invoked by any party in the future. In essence, the Waitangi Tribunal, Labour, Te Pati Maori and the Greens may have inadvertently presented a legal path to invalidating the Treaty of Waitangi. 

Correction

I was curious about the veracity of this so I asked a lawyer (anon) and received an answer that basically boiled down to. The Treaty of Waitangi was not a treaty under International Law because it was not between states, so international law is not applicable.

It is an interesting idea about how fighting for perceived rights might invalidate the basis on which they are fought. But in this case, not correct.

Image: Linda Munn, Jan Dobson and Hiraina Marsden. Linda Munn was the only one still alive in early 2010., Public domain, via Wikimedia Commons.