Routing works excellent on my Nuvi  except when the Start/End points are in different countries; if it is the case:

1. the device takes a lot (minutes) to calculate the route - also if the two points/cities are pretty close, while for routes within the same country takes seconds.

2. the route to follow (purple) is mostly translated from the real streets, a picture ( http://imageshack.us/photo/my-images/401/garminrouteissue.jpg/
 - sorry for the quality) better explains the behavior: the red street is the highway, that's the only possible way. The purple line is the displayed route, as you can see they are not matching.

This happens only when start/end points are in different countries. Picture is taken routing from Bolzano, Italy to Innsbruck, Austria.
I create gmapsupp from geofabix's pbf files, I tried today with mkgmap version r2306, but I experienced the issue as well with  older versions I tried with. I use standard command lines option only "--route --remove-short-arcs --add-pois-to-areas --index --gmapsupp". Bounds are from navmaps.eu

Any clue?

Thanks!
Enrico