I didn't find this one here so I am writing now...
I have M3 8 GB with FW T 2.003.4 (CZ/SK/EN) and it has following bug:
If you configure main menu not to show
Backlight Timer option, this line will remain in main menu, but on the other hand the option
Settings will
disappear. So than there is no other way than hard reset of the device and losing all data... I haven't tried that new FW T2.003.5 because except of this it works fine (at least I am still testing it, because it's my new baby

).
Does the new FW have the same problem? But make backup before trying