Hi,
I have a "bad" 64s with the same problem
The unit was already remplaced by Garmin but the new unit do the same
Still waiting for a new firmware with you
I post this message on a french GPS forum :
http://www.sorcieremonique.com/t15714-gpsmap-64-family-et-geocaching#141259
I hope to hear something new as soon as possible from Garmin !