Hi Stuart - directions are generated as you plot, so I'm afraid the "Same Route Back" feature can't reproduce directions in reverse, it can only copy the points you plotted on the outbound stretch. You would need to plot the route back in the normal way if you needed the directions for the return leg. Unfortunately, I don't think there would be an easy way for us amend the site to do this automatically.
If I plot a route out to a destination and then open the toolbox and select "same route back", the exported file will only contain turn-by-turn directions for the first half of the route. If I want directions for the return journey, I must manually plot it:
Is this a bug, or simply an undocumented feature waiting on the backlog? :-)