I think this is due to either weak gps antenna or bad software/mapping. Occasionally when i am on the highway, the blue dot will veer off the highway and into a building half a mile off the road. I am not sure if this is because the maps are drawn/rendered badly, or if the antennae is just innacurate in some spots. Whatever the reason, you are not alone.
I would turn GPS on and locate yourself, then take a drive down the street and see if it adjusts properly.
I was in houston a few days back and i left a restaurant and tried to locate myself and it placed me halfway across town, but after driving for about half a mile, it relocated to my correct position. I think it is just spots here in there that it doesn't like, but it does require some testing.