by Enrique Castro.
Hi:
I got a this bug in assign 2.3 for a while: when changing a grade for a previouslu graded submission the old feedback comment and files did not got loaded in the grading form. Thus, if saved, the submission comment and files would be overwritwen with blank values.
But now with Moodle actualized to 2.3.1+ (Build: 20120823) the problem is gone: grades with feedback comments and files can be edited repeatedly.