Many nationalists in Quebec are actually federalists. What it means is that they want that Quebec remains part of Canada, but they want also to be sure that the French-speaking people have some serious protection against anglo-conformity, something that is perceived as a deep-seated reflex in English Canada. Pierre Trudeau followed the same logic by introducing the Official Language Act, and many other policies. And when he wanted to give a veto to Quebec (but also to every province), he was still following this logic. Strangely enough for some, Trudeau was also a Quebec nationalist. He actually fought the independentist version of nationalism.
Harper and the Conservatives, who are much more open to decentralization of powers for the provinces followed a logic of working with the nationalists. So did Mulroney before.
So, what is the NDP doing? The same thing. They try to work with Quebec nationalism, emphasizing the federalist version, but the main difference is that they are benefiting from a fatigue towards the independentist version. Will it open a can of worm, in time maybe, but it is probably better to address the issue directly by working with the nationalists. This is much more constructive, and this is what people in Quebec are seeing in the NDP.
Maintaining something that looks like anglo-conformity from a Quebec perspective, simply by ignoring the issue long enough, is actually opening a bigger can of worm.