Setting the "No Overwrite" on one-way arrows causes them to be drawn even where there's no terrain. Additionally, the arrows drawn where terrain is absent don't get recolored correctly. One-way arrows under such circumstances are still correctly not drawn on terrain that has the "allow one way" flag off.
Of course - the bigger question here is, should that option be allowed at all for one-way arrows? It has no effect in-game anyway.
