I just joined this forum after downloading and installing OSM to my MapSource. So far so good.
Then I created a route to the new map but I keep seeing straight lines from one via point to another, despite the settings in Preferences (CTR-SHFT-P).
Did I miss something?
It also could be a setting in your Garmin (friend of mine once had the same problem). It just drew a straight line from the current position to the destination. So check your transport settings.