Unable to choose an alternative route than planing a round trip

Im planning a route from Solingen (Germany) to Trier (also in Germany) and your app is planing the shortest route, but this route isn‘t using the highway all the time so I would like to choose an alternative route which is shown on the screen. But I cannot choose this alternative route for both trips. For the return trip your app still wants to use the shorter route, that I don’t want to use.