Has anyone experienced the satellite navigation go blank with good 3G reception. This has happened a few times, I come out to the car and everything boots up. The sat nav is working it shows 2 or 3 or 4 bars the I drive away and in 5 minutes the screen goes blank (gray) and I notice the bars do not change even when I know I should not have 4 bars. What seems to happen is that the nav freezes up and unless I reboot the main screen I do not get the nav back. Once I reboot the signal starts to work and I have the satellite nav back. Any ideas?