Import activities creates copy of existing roles

Each time when a user imports an activity to a course, two new roles are created: editingteache_1, student_1. If these exist, then editingteache_2, student_2. No users are assigned to the role, but it is quite annoying to remove them as administrator each time. Moreover, they appear in list of roles averywhere. See also this forum thread: http://moodle.org/mod/forum/discuss.php?d=62166