On the OSM forum, we get: http://forum.openstreetmap.org/viewtopic.php?id=3879 The report says:

when a border overlapes a street, the street is broken. The street is not recognized for routing. This happens in MapSource and on the Oregon 200 device.

This must be because in the style file, these lines are at the top: aeroway=runway [0x27 resolution 20] boundary=administrative [0x1c resolution 18] boundary=national [0x1e resolution 17] boundary=political [0x1c resolution 17] and so the way, which is tagged as both a road and a boundary, has garmin code 0x1c (not a road code). Personally, I think the highway tag should take precedence over the boundary tag and these lines should be moved below the highway stuff. Whaddyathink? Cheers, Mark