There is big bug about notification function in assignments. When a teacher give grades and comments in assignments, the email notification will be sent to students, when the "notify students" is set to "No". Below is the detailed description of this bug.
First, I create an assignment and leave the “default setting for “notify stdents” to “No”. And save the changes.
Then use a test student account to upload a submission in the assignment. Then I use a teacher account to grade the assignment by clicking “grade” in the assignment.
Then, the teacher click “save” and do not tick the “notify students”.
However, the assignment still sends email notification to students about the grades. It is quite confusing to teachers. Since it is a core function in Moodle and many teachers are using it, I hope it can be solved as soon as possible.