Hi Bob,
It's hard to give a specific answer without specific data. But it sounds like the problem is in the map data. The behaviour you describe usually occurs if the router cannot find a physical connection in the direction it wants to go so it is forced to find a way around the "break" in the data.
Garmin's maps use the same supplier, Navteq, for the data. It would be interesting to have the start and end points to try and see if they produce the same round-about routing in Garmin's maps. If you're shy about sharing your address -- and you should be -- you could pick a start point in the same general area (lat/long coordinates or the intersection cross streets from a nearby mall or gas station would work), ensure that it produces the same silly routing and share those start and end points so we can have a look at them.
...ken...