To reproduce the problem follow these instructions:

1. Enrol 1 teacher and 4 students (A, B, C, D)
   Create two groups and enrol students A-B in the first group and students C-D in the second one
2. Create a new assignment
   Group submission settings > students submit in groups > yes
   Grade > Grading Method > simple direct grading
   Grade > Use marking workflow > yes
3. Log in as student A (Group 1) and make a submission
4. Log in as student D (Group 2) and make a submission
5. Log in as teacher and mark student A and student D, then set workflow status to marking completed
6. Click "view/grade all submissions", select all students and select "set marking workflow state" and click go. Set the state to released and save changes.

Grading overview
The final grade column is filled only for student A and student D (group members who submitted the assignment) : grades will not be visible to the other students in their respective groups.