What really annoys me most about this is that it was completely unnecessary. No legislature can bind its successors and the statute guaranteeing those pensions could have simply been repealed. Getting the federal court to do it was an act of political cowardice and the cost will be a marginal but permanent reduction in state sovereignty.
The powers not delegated to the United States by the Constitution, nor prohibited by it to the States, are reserved to the States respectively, or to the people.
The governance of bankruptcy is an Article I power of the Federal Government.