To replicate:

1. Enrol in a course as a user you can receive notifications for
2. Add an activity or resource to that course, check the "Send content change notification" option
3. User will receive the notification
4. Disable Send "Course content changes" notification in Site administration > General > Notification settings (remembering to scroll to the bottom of the page to save changes)
5. Add or edit an activity on course
6. Check the "Send content change notification" 
7. No notification received

While the above does not do anything incorrect, it is confusing because the teacher checking the "Send content change notification" is unlikely to know the overall notification settings or have control over them. They have every reason to expect a notification to be sent out when they check that box, but it never will be.

My suggestion is that "Send content change notification" checkbox should not be visible if the notification type is disabled. This is consistent with many other features in Moodle (if a feature is disabled, the associated controls disappear).