Once completed, lock score by checking self.completed

mentoring/mentoring.py

@@ -148,6 +148,8 @@ class MentoringBlock(XBlockWithLightChildren):
         elif completed and self.next_step == self.url_name:
             self.next_step = self.followed_by
 
+        # Once it was completed, lock score
+        if not self.completed:
             score = sum(r[1]['score'] for r in submit_results) / float(len(submit_results))
             self.runtime.publish(self, 'grade', {
                 'value': score,