Given all the discussions about the logic of the reducing, why don't you make a little change to the kata description? Something like this:

The Mars Pathfinder has a circuity malfunction and can't do a 180º turn, only going forth, turn 90º left or right, you're given an initial path and you have to remove those turns so the final path is still doable.

Or something like that, what do you think? Is it any better?

I think that you should read all the description (including the Notes) and not only that sentence to get what is expected to do.

Ok, but in the description you are saying that: "Going to one direction and coming back the opposite direction is a needless effort". But if you travel in the shape of a box, and then return to where you started, you are doing a needless effort. I think the best plan in the case NWSE as in NSWE is to stay in the starting point. What do you think?

NWSE takes no reductions, so you travel in the shape of a box, and you return to where you started.

NSWE has two consecutive opposites, so there are two reductions, and you do not travel at all.

There is a test that doesn't make any sense. If you go North, West, South and finally East yo go back to the same initial point, and as the problem says the opposite directions neutralize each other. So Nort - South and West - East keeps you in the same point.