In a course, when you click on the Enrol cohort button located on the Enrolled users page, the default role is Manager.
When you enrol a cohort from Enrolment methods, the default role is Student.
Because most of the time, you wish to enrol students to a course, the default role should be Student. I think it was a few weeks ago but I'm not sure.
By "mistake", all the managers of my Moodle 2.0 platform enrol students as Manager because of the default role. Additionally, they consider the way to unroll a cohort difficult to find (from Enrolment methods).
Thanks for fixing that.