for every outpost I use a train stop (name is always "Support") for the daily needed stuff (Turrets, Repair Kits, ...). If a outpost runs short on some item, it sets the train signal of his station to green and sends a signal to the main station (A). The support train calculates a path to the open "Support" train stop and delivers his cargo. This works fine for all stations, except for B.
If B opens his station, the trains always calculates a route to C (that is closed!). Why?
When the trains waits before C, I always have to say to the train "go to main" after passing C "go to support". After this it finds his way.
I lost three trains, because they were waiting outsite of this outpost
