Discovered while testing http://tracker.moodle.org/browse/MDLQA-5179

Steps I've followed:

• I've created an assignment with grade = 90 and using marking guide as grading method
• I've created an associated marking guide with one single criterion with maximum mark = 90
• I've graded a student submission with 45 / 90 in the only criterion of the marking guide, so his/her grade is 45/90
• I edit the marking guide and I set 100 to maximum mark in the single criterion I have
• I confirm the changes selecting "Do not mark for regrade"
• I see this warning message: "WARNING: Your marking guide has a maximum grade of 100 points but the maximum grade set in your activity is 90 The maximum score set in your marking guide will be scaled to the maximum grade in the module. Intermediate scores will be converted respectively and rounded to the nearest available grade."
• I go to the student submission and the mark of the marking guide are 45 / 100
• I edit the assignment grade in the assingment settings page, when I change the value I see this message in a JS window: "This assignment has graded submissions and changing the grade will not automatically re-calculate existing submission grades. You must re-grade all existing submissions, if you wish to change the grade." and I submit changes
• The student submission grade is 45 and the grade of the marking guide criterion is 45 / 90
• I edit the marking guide setting the maximum mark to 100
• The student submission grade is 45 and the criterion score is 45 / 100