git grep -a doesn't find string in binary file

I have a binary file with the string 'SEGMENT4' inside:
    $ strings AR/reports/BMCD_AGED_AR_CUST.rdf | grep -i segment4
    (CC.SEGMENT1 || '\n' || SEGMENT2 || '\n' || SEGMENT3 || '\n' || SEGMENT4 ...

grep sees it:
    $ grep -li segment4 AR/reports/BMCD_AGED_AR_CUST.rdf | wc -l
          1

git grep does not:
    $ git grep -a -li segment4 AR/reports/BMCD_AGED_AR_CUST.rdf | wc -l
          0

What am I missing?

Here is my environment info:
    $ uname -a
    MINGW32_NT-5.1 B8058 1.0.12(0.46/3/2) 2010-02-05 01:08 i686 unknown

    $ git --version
    git version 1.7.0.2.msysgit.0

Thank you,
Phil Lawrence