All contracts, treaties, agreements are under-determined. Why would there be courts, if not for lack of clarity? Whether the under-determined nature of arrangements backed by law in general is inherent or deliberate is worth thinking about. But we can be quite sure that the under-determined nature of the European Union Treaties is their modus operandi. They were written thus to cover objection from just about any direction to anything within them we care to think of.
So when the Bundesbank's Jens Weidmann calls into question the precise mandate of the ECB, by questioning the German constitutionality of OMT, a great fissure opens in the common front of europhile argument that the Treaties set out the rules. And not just for Article 123 where, as he amiably admits,
"...there are few countries in the currency union which place such a high worth on article 123 as Germany." However, as he goes on, "There would be a very wide discussion on what else could be changed, apart from the mandate of the [European] Central Bank."
Any EU member-state choosing to determine the constitutionality of European requirements under their own constitution and before their own constitutional court without, as Germany never has (and Hell would freeze over before it did), referring to the ECJ, has means to resolve deliberately under-determined EU Treaty statements, and in conformity with their own constitutional requirements.
For the United Kingdom, whose whole approach to constitutional determination is flexible to the point of idiosyncrasy, the German challenge to the EU treaty-drafters cunning plan may yet facilitate the growth of a UK constitutional spine.