Hi Johann,
It's time to eat humble pie. I managed to create a single tile with all the places and roads on that I've been testing and this chooses exactly the same route as the inter-tile file. It seems it was just a coincidence that the routes hit the motorway around the tile boundary.
Sorry, my testing gaves other results. If I create a map with two tiles, then border crossing takes place at a secondary street with a rather inoptimal route. If I compile the same map into on single tile, then routing works as expected.
So i conclude that definitely something with the inter-tile routing gets wrong. It is not the osm data.
All tests are done on a etrex venture, as I have no running mapsource here.
Fine, I believe you. Unless you provide some example data to inspect, it's hard for us to guess what's wrong. Please provide the detailed info. Cheers, mark