I'm not sure what I did here, but I was placing an embankment loft under the track, when suddenly the arrows turned to squares and prevented raising of the loft. Then when I clicked on the exit cross at the top right of the screen, it just closed the program without saving.
What did I do to cause this? It was done unintentionally, (it could have been a hotkey) so not sure what I may have done in the normal procedure of clicking on track etc.