grub fails to detect harddrive on freebsd 5.0-release

[leon j. breedt]

os:     freebsd 5.0-release

grub version: 0.92 (freebsd port)

gcc: 3.2.1 [FreeBSD] 20021119 (release)

extra cflags:
    -O -pipe -march=pentium4

hard drives:
ad0: 76319MB <WDC WD800JB-00CRA1> [155061/16/63] at ata0-master UDMA100
ad1: 78533MB <IC35L080AVVA07-0> [159560/16/63] at ata0-slave UDMA100

description:
    i run the 'grub' command in interactive shell mode. i try to
    force detection of ad0 as '(hd0)' using 'device (hd0) /dev/ad0',
    and get no error message. i then execute 'root (hd0,2,a)', as
    a precursor to running 'setup (hd0)', and get the error message:

    Error 21: Selected disk does not exist

    however, grub does detect the ad1 disk as '(hd1)'.