Why an Agile Project Manager is Not a Scrum Master - Johanna Rothman
The project manager and product owner start the release planning and ask the team if the release planning is ok.
The real difference is the difference between a Scrum Master and an Agile Project Manager. A Scrum Master is not a project manager. A scrum master does not manage risk by him or herself. A project manager will take on the risk management responsibility without asking the team.
A Scrum Master has only allegiance to the team. A project manager has responsibility to the team and to the organization.
An agile project manager is a project manager. That means he or she is actively studying project management, which means he or she is studying lean also, looking into work in progress. (I realize many project managers do not actively study project management.) I have high expectations of an agile project manager, and that is to limit WIP, work in progress, to measure cumulative flow.