Miscalculation of teacher's re-assessed submissions (workshop)

Submission X should be rated 0-10. Assessment of X should be rated 0-5.

Student A rated X as 10, Student B rated X as 10 and Student C rated X as 6. 
Submission X average grade was calculated by Moodle as 8.7

Student A assessment was rated 5, Student B assessment was rated 5, Student C assessment was rated 3.2.

Teacher saw 4 points difference (40%) between assessments, re-assessed Submission X and rated final grade as 6 (overriding former grade 8.7).

Expected behaviour: Moodle should correct assessment grades of students A, B from 5 to 3.2, and C from 3.2 to 5, but it does not!