Just tested this on my local moodle 1.8.7 install with the following scenario.
Questions A and B are originally worth 1 point each.
- In the quiz, student John got 0 out of 1 for question A and 0.5/1 for question B.
- Teacher overrides the mark for question A and sets it to 0.5.
- Then teacher edits Questions A and B and counts each of them for 2 points.
- Then teacher regrades the whole Quiz.
- John's score for Question A is now worth 0.5 out of 2. This is questionnable.
- His score for Question B is now 1 out of 2. This is OK.
Conclusion.- Scores which have been manually over-ridden do not change (i.e. they keep their over-ridden value) when a Quiz is regraded. This behavior may be considered correct or incorrect depending on your point of view. I would hold the view that it is incorrect because, if a teacher decides to over-ride a score on an individual question and changes e.g. 0/1 to 0.5/1 it means that he deems that the response was worth half the points. If the score awarded to that same question is later on changed from 1 to 2 and the quiz is regraded, teacher would expect the final score for that question to keep the "half marks awarded" value when overridden, so it should be regraded to 1 out of 2.