When group member A submits for grading, he still got the "Edit submission" button, and status is "Draft" but there is no submit button.
Fellow group member B gets status "Draft (not submitted)", but both "Edit my submission" and "Submit assignment" button. Assignment is set to not require all group members submit.
The teachers view shows "Draft (not submitted)" for student A who submitted, and "No submission" for the other group member B.
Log shows that student A did click "Submit for grading" button.