syslinux variant of make-live-device.sh not working

[Claude Heiland-Allen]

when it gets near the end the script reports something like this:

...
2369015 blocks
~/code/puredyne/bouilloncube/sh/syslinux /mnt/make-live-iso
[*] syslinux configuration
syslinux: this doesn't look like a valid FAT filesystem
...

and indeed the filesystem cannot be mounted with -t vfat option.

I'm guessing it occurs around these two lines:

cat /usr/lib/syslinux/mbr.bin > ${2}
syslinux ${2}1

the grub2 script seems to work fine with the same SD card (completes successfully - haven't had a chance to boot it yet, if it fails I'll report back)

tested on up-to-date Lucid