Strange assignment grading issue or submission listing screen bug

by Toan Tran.  

We encountered a strange issue with assignment grading:

A student's grade will only show 50/50 on the submission listing screen regardless of what grade I change it to.  This happens whether I changed the grade in the grading screen or quick grade from the submission listing  screen.  However, the grade book will reflect the new grade as soon as a new grade is given.  The grade is not overridden in the grade book.

This does not happen to any other student or assignment.  

Please see screen captures attached:

1. Teacher view in grading screen (1st picture) shows the correct grade of 48/50
   
2. Teacher view in assignment submission listing screen (2nd picture) shows 50/50 regardless of quick grading is on or off.
   
3. Grade book (3rd picture) shows the correct grade of 48/50, which matches the 1st picture.
   

Has anyone encountered this issue or can shed some light on this subject?  We are using the newer (2.3+) assignment module running on Moodle 2.5.  This is an "Online Text" assignment.

Thanks,

Toan