Seat Leon 21 plate, in-built satnav.
Went out today to a location about 10 miles away, I used the route guidance to get there. When I got in to come home the satnav thought I was already at home, and then as I drove back (general westerly direction) it thought I was driving south from home, so now it thinks the car is 10 miles away to the south (in order to get there, I apparently drove through a couple of parks and a factory, and across a large river 
).
Tried the obvious of restarting the car, but no joy. Next plan is to leave it overnight and try tomorrow - at least I don't have to go anywhere this week
.