When creating a new course with manual enrollments enabled, if the manual enrolment plugin
Notify before enrolment expires (enrol_manual | expirynotify) setting is set to "Enroller + Enrolled" (or the new "Teacher + Enrolled user" language string in 3.6), the course manual enrollment instance will default to "Enroller".  You would expect it to be set to "Enroller + Enrolled" to match the default.

 
This looks to be caused by the call to add_default_instance in https://github.com/moodle/moodle/blob/master/enrol/manual/lib.php#L128.  It looks like the code was borrowed from get_instance_defaults in the the self-enrol plugin (https://github.com/moodle/moodle/blob/master/enrol/self/lib.php#L337), which correctly sets the course expirynotify to Enroller since, in Self-Enrol, the Enroller and Enrolled are the same person, and you would not want them to receive two notifications.