In course/info.php the call to get_role_users() is returning students+teachers for display in the list of teachers.
It seems the test for is_int($roleid) in get_role_users() is failing.
Calling get_role_users($roleid+0, ...) will cause the $roleselect sql fragment to be created and the function
returns the expected results (with roleid=3 in this case).
Entered as a possible security issue as students != teachers