This might happen when you are moving on a narrow street and the blob shows you on the side of the street (on top of the building for example). This situation happens because on a narrow street all the satellites the device sees are in lined up. So it estimates signal accuracy as high, but the location is actually slightly off. Specifically the location is good in one direction (along the street), but might be off in another direction (perpendicular to the street).

What to do?

Avoid setting locations onto narrow streets with tall buildings.
If you need to do that make sure the radius is sufficiently big (20 or more meters).
Be warned that if the signal quality is low the location might not activate at all.