./lib/grade/grade_item.php:
/**
* If set, the whole column will be recalculated, then this flag will be switched off.
* @var bool $needsupdate
*/
public $needsupdate = 1;
also:
/**
* Performs the necessary calculations on the grades_final referenced by this grade_item.
* Also resets the needsupdate flag once successfully performed.
*
* This function must be used ONLY from lib/gradeslib.php/grade_regrade_final_grades(),
* because the regrading must be done in correct order!!
*
* @param int $userid Supply a user ID to limit the regrading to a single user
* @return bool true if ok, error string otherwise
*/
public function regrade_final_grades($userid=null) {
This would seem to suggest that it is to do with the re-grading process.