MMC Mount Problem

I am testing a new MMC device driver for an embedded target under
2.6.13.x and cannot mount the MMC drive.  The symptoms are consistent
with the kernel reading sector 0 from the card and treating it as the
boot sector, which is actually sector 32.  The partition table in
sector 0 correctly points to the main partition starting at sector 32.
Any ideas on why the kernel apparently thinks sector 0 is the boot
sector?

When I type:

    sh-3.00# mount -t msdos /dev/mmc0 /mnt/mmc

I get the following error report:

    FAT: invalid media value (0x01)
    VFS: Can't find a valid FAT filesystem on dev mmcblk0.
    mount: Mounting /dev/mmc0 on /mnt/mmc failed: Invalid argument

The first report is from fat_fill_super() in inode.c.  The
fat_boot_sector structure there contains the following values, which
match the corresponding fields in sector 0:

    b->sector_size[1:0]: 50 07
    b->sec_per_clus: 1f (31)
    b->fats: bf (191)
    b->dir_entries[1:0]: 06 00
    b->sectors[1:0]: 00 b9
    b->media: 01
    b->fat_length: a5f2 (42482)
    b->secs_track: 1dea (7658)
    b->heads: 0006 (6)
    b->hidden: 07bebe00 (129940992)
    b->total_sect: 3c8004b3 (1015022771)

I have confirmed that the only MMC operations performed during the
mount are a single block read to address 0 followed by a status check.