Encontrou uma solução.
Parece que o mpg de origem não estava sendo convertido em um arquivo VOB totalmente compatível. Eu resolvi isso com o seguinte script que re-muxes o arquivo de origem antes de construir o DVD:
#!/bin/bash
# Burn an MPEG file to a DVD as a looping demo
# Author: SpliFF (www.warriorhut.org)
# License: Public Domain
# Usage: mpeg2dvdloop input_file [project_name]
# Path to input mpeg file
INPUT="$1"
# Name of DVD project (default taken from input filename)
INPUT_FILENAME="${1##*/}"
NAME="${2:-"${INPUT_FILENAME%.[^.]*}"}"
# DVD burner device (might be /dev/sr0, /dev/dvd or /dev/cdrom, etc)
DVD_DEVICE="/dev/sr0"
# Working directory (make sure it has plenty of space)
# You'll defineatly want to change this if /tmp is a tmpfs ramdisk
WD='/tmp'
echo "Creating DVD project \"$NAME\" in \"$WD\" ..."
echo -e "\nWriting dvdauthor config file to \"$WD/$NAME.xml\" ...\n"
cat > "$WD/$NAME.xml" <<_EOF_
<dvdauthor>
<vmgm />
<titleset>
<titles>
<pgc>
<vob file="$NAME-remux.mpg" />
<post>
jump title 1;
</post>
</pgc>
</titles>
</titleset>
</dvdauthor>
_EOF_
echo -e "\nExtracting audio and video to elementary streams using transcode tools ...\n"
# Gentoo package: media-video/transcode
tcextract -i "$INPUT" -d 10 -t vob -x mpeg2 > "$WD/$NAME.m2v"
tcextract -i "$INPUT" -d 10 -a 0 -x ac3 -t vob > "$WD/$NAME.ac3"
echo -e "\nMerging streams into compatible file using mjpeg tools ...\n"
# Gentoo package: media-video/mjpegtools
mplex -f 8 -o "$WD/$NAME-remux.mpg" "$WD/$NAME.m2v" "$WD/$NAME.ac3"
echo -e "\nCreating DVD structure using dvdauthor ...\n"
# Gentoo package: media-video/dvdauthor
rm -rf "$WD/$NAME-DVD" && dvdauthor -o "$WD/$NAME-DVD" -x "$WD/$NAME.xml"
echo -e "\nBurning to DVD-R using growisofs ...\n"
# Gentoo package: app-cdr/dvd+rw-tools
growisofs -v -Z "$DVD_DEVICE" -dvd-video -V "$NAME" "$WD/$NAME-DVD"