Thanks for the new example, now I can understand better what happened.
Note that: import route = new route = new navigation.
Navigation currently cannot start on the last route leg (after the last waypoint).
This is to help with complaints that navigation ends when it starts in round trips,
because start and end points are near, so the exit and entry paths are the same.
The flexibility you want to get in / out anywhere on the route has its drawbacks.
If there is better solution - which can be applied mathematically - I could see it…