Our software dev team is currently using kanban for our development lifecycles, and, from the reasonably short experience of a few months, I think it's going quite well (certainly compared to a few months ago when we didn't really have a methodology).

Our team, however, is directed to do work defined by project managers (not software project managers, just general business), and they're using the PMBOK methodology.

Question is, how does a traditional methodology like PMBOK, Prince2 etc fit with a lean software development methodology like kanban or scrum? Is it just wasting everyone's time as all the requirements are effectively drawn up to start with (although inevitably changed along the way)?