If user's have UTF-8 character names (e.g. non-latin or accented characters), then the roster export garbles their names. The names should be exported as (ascii-encoded) UTF-8 characters.
Steps to reproduce:
(1) Create a student user who's name has accented or non-latin characters (e.g. Japanese)
(2) Select 'All Grades'
(3) Select 'Export Gradebook'