Resource Assignments between project and workplan

In Project Management/Project Resource Management, there seems to be no connection between roles assigned to the project and roles available to be assigned to tasks in the workplan, and vice versa.  For example, one can assign roles of functional lead and DBA to the project and then assign people to these roles.  But when creating workplan tasks and assigning roles to the tasks, the list of roles is not limited to the ones assigned to the project. 

By the same token, if the assignments are executed in reverse order, i.e., roles assigned to the project plan followed by roles assigned to the project, one would expect (I think) that the roles assigned to the tasks would already appear as roles assigned to the project.  However, this is not the case.