I have reported this to moodle bug tracker
http://tracker.moodle.org/browse/MDL-9998
MDL-9998: When two students with same name and appear together in assignment table, moodle does not display the name for the 2nd student.
File(s) effected: /mod/assignment/lib.phpFunction/Part of file effected: display_submissions()
Suggested change: comment out the following two lines:
//$table->column_suppress('picture');
//$table->column_suppress('fullname');
Hope this could go into the core, thanks!