When copying and pasting train signals from a straight track to a diagonal track, the pasted (new) train signal on the diagonal track doesn't work.

I tested this by placing a horizontal train track with signals. Using the copy tool to copy the train signal, then paste tool on to a diagonal adjacent ...

Never tried this before and it seems broken so assume it's a bug, not a feature

tl:dr You can place train tracks from the map view infinitely (if there are no obstacles/water in the way) even through unexplored areas

Steps:
Place track normally near the player
Whilst holding track, click the green ...