GPS Error?

[GC8]

Has anyone experienced a GPS receiver being incorrect before? Allow me to expand on that: I don't mean a satnav thinking that youre driving on a parallel road, 10m margin of error or even selective availability (I was an early adopter, so this used to be an issue), I mean 'Tomorrow Never Dies' levels of GPS inaccuracy, where a dedicated GPS receiver believes that I am in a different location to two separate satnav devices which are both successfully overlaying a map with my correct location on it.

The difference wasn't quite as great as in the film, but if The Man was using that location for a Predator drone strike Id have been sufficiently far enough away to enjoy the fireworks without any danger.

The Garmin hasn't been turned on for a long time and Im wondering whether the GPS week rolling over and some leap second corrections may be causing it to misplot, but the only (possible) clue is that the time is within one second of UTC time, but its 15 seconds different to GPS time converted from week-seconds.

[JimmyTheHand]

I have seen errors of 1km on an old 8 channel hand held device which would adjust itself over a few minutes and issues if wrong world model selected - I have also seen a TomTom think it is 100 mtrs or so out, such as it thought it was in fields not on the road (reboot sorted it)

But I'd guess if it hasn't been on for a while then the Almanac hasn't been properly downloaded - it should reset if left on for an hour or so.

[Grandfondo]

My Garmin (bike) plotted a course saying I traveled 750km in a straight line when in reallity I did a 44km loop!