Hi!
I have just updated my Vista HCx today, and came across the same issue:
1) Power on
2) Hit menu (lower left button) on the satellite screen
3) Shutdown
This is bad for me as I am used to press that button to go to the cache search (even if the GPS has no satellite fix yet). Also, I use it to go to the main menu to do some stuff until it has the fix.
Regards,
Leloup