UX practitioners -- such as UX Designers, IAs or UX Researchers -- typically consider understanding the user's needs as part of their role.
By extension, UX practitioners often define some, or even many, of the requirements on their projects.
When working with Product Managers however, the task of "owning requirements" is typically seen as the PM's responsibility.
To what extent should the UX practitioner get involved with defining requirements when working with a Product Manager?
This is my main question, but here are some related questions to help illuminate the topic:
Is this an area that becomes the Product Manager's "territory", to which the UX person should defer -- just at the PM perhaps has to defer on UX matters?
Obviously there will be some overlap, but how do you know when you've got the balance right?
How do you avoid friction and preserve harmony within the team, such that everyone understands their roles and responsibilities?