sgtfrog,
Sounds like a power reset in your case, where the ship's power to the unit fails momentarily, setting you back to start.
The "typical" gps problem is certainly not anything where the satellite reaches into your set and changes its pages, since they simply can't do that. Such failures are surely inside the receiver itself (a likely place, where mechanical switches abound, and vibration setting them off is a common failure mode.
Typical failures are where the satellites are in odd corners and the nav solution stinks - usually flaged by raim or by a poor signal or poor nav flag.
Signs of jamming are usually where the system cannot lock on the satellites and dumps its nav solution (spoofing a GPS to "shift" the solution is so difficult, it is automatically awarded a PHD in EE).
Here is an example of an inadvertant jammer - its effects and cause.
http://www.gpsworld.com/gpsworld/art...l.jsp?id=43404
Let each one with a problem identify the model/make and also if the system was certified on installation by the FAA/CAA/KGB
