Changes and playlist are lost after restart

After restarting Voyage MuBox, all my previous changes to MPD are lost

This is a known issue in Voyage MuBox software if you restart the box by unplug and then re-plug the power. The most proper way is to issue a halt command via ssh or serial console to shutdown, or use reboot command to restart the box gracefully.
However, you can implement periodic saving data to disk so that it could recover from sudden power lost. In webgui (e.g. or voyage-mubox.local), go to System -> Cron and add the following entries:

# m h dom mon dow command
*/5 * * * * ( /etc/init.d/voyage-sync sync )

Then, edit (use nano or vi), /etc/default/voyage-util and appends the following lines to the file:

VOYAGE_SYNC_RECOVER="YES"      
VOYAGE_SYNC_RECOVER_DIRS="var/lib/mpd"                            

Or simply append the above lines using command line in ssh or serial console:

echo "VOYAGE_SYNC_RECOVER=\"YES\"" >> /etc/default/voyage-util
echo "VOYAGE_SYNC_RECOVER_DIRS=\"var/lib/mpd\"" >> /etc/default/voyage-util