If you:
- put a train in a location where it cannot path to anywhere (in my case a dead end)
- open up the train gui (hit e while hovering the train)
- try to path somewhere and it says on path
- leave gui open and switch to manual mode
- reverse until you now have a path
- temporary station still says no path
You have to come to a complete stop before it recognises that you can now path to where you are trying to go