Hi, my mio does the same, even when activesync isn't running...
Mine is also a GPS satnav unit and we lost everything (including our route home from France !)....so I hunted down and purchased this software
http://www.spritesoftware.com/backup.php which WILL get you out of the s**t - as it has me on several occasions....
It is really easy to use, very cheap (around £18) and if it doesn't work they will give a full refund - I bought the wrong version at first.
Backup to the storage card, opt to make it a .exe file and backup in about a minute.
After powering up from a dead PDA, it will restore
EVERYTHING in about one minute,
exactly like it was when you backed it up.
......and you can also keep a backup on your PC as well.
I cannot praise this product enough !
Hope this at least helps.