The OMA and the province were both sophisticated parties in the 2004 negotiations.  It should not have been lost on the OMA that the feds were not at the table and that the province could not guarantee the behaviour of the feds in the future.  The OMA acccepted the risk that federal policy might change.  13 years later, it has.  Suck it up.  

I am paying 54% top marginal tax rates, why should you be allowed to sprinkle your income across your family when I can't.