Straight line route over long distance in MapSource

I posted the following on the Garmin MapSource forum recently: ‘I have successfully got to grips with routing in MapSource today, except for one thing: whereas routes over short distances like 30 miles follow the road and display driving directions correctly, routes over longer distances like 100 or 300 miles show as a straight line. I am using OSM World Routable maps and my MapSource version is 6.11.6 (I know it’s three years old, but it has always been sufficient for me).’.
This was the reply: ‘I am afraid we cannot provide support for third-party maps and there could be all kinds of reasons why the routing does not work. If you really don’t want to use the newest 6.16.3 version, I would at least use 6.13.7 though (…ource_6137.exe), maybe that version actually fixed the route bug.’.
I installed MapSource software version 6.16.3, but the routing results were just the same. I responded tp this effect in the Garmin MapSource forum and received a further reply: ‘Thanks for reporting back, and for checking out 6.16.3. Not trying to be snarky, but then it really looks like the OSM map is bad. Routing over long distances works pretty well for Garmin maps. Have you tried reporting this to the creators of the OSM map? You can try bringing this up in some OSM related forum and see what they say.’.
I should appreciate anyone’s input.

Hello Silver Mapper,

Same thing here, latest Mapsource and latest talky toaster OSM maps.

It does work however if you put a few via points in the route. I just tried a 200 mile route and had to put 2 via points in it to make it work properly. Not perfect but it does work, for me anyway.