Student grade feedback is showing from different courses.

To see how many feedbacks are out of sync I run the following query:

SELECT 

  fb.`assignment` AS fb_assign,

  ag.`assignment` AS grade_assign

FROM

  mdl_assignfeedback_comments fb,

  mdl_assign_grades ag

WHERE 

      fb.`grade` = ag.id

  AND ag.`assignment` != fb.`assignment`;

On our installation I had more than 1000 records. I could not run a simple update to use one specific assignment id because the right one was interchanging.

I was trying to find the code where this could happened without luck. This make me think that it must be happening during the upgrade to the new question engine Moodle 2.3.1.