@Kunix.
When you flash a lower version (downgrade) using pre-boot or Gupdate.gcd it seems to clear Nonvol automatically at first boot.
I've managed to fix some strange faults on Nuvi's this way. (going back to a very very early version)
I fixed one bricked 1350 this week by flashing JAP and immediately after flashing US in preboot mode.
I think that maybe the owner had been experimenting with Asian Firmwares.