Go Left, Nikki!

I just got done free lunging Nikki, insisting that he only go to the left.  To my surprise, he trotted to the left, around and around the arena quite happily.  Why won't he do that on lunge line?!  I'm mystified. 

After a few minutes, he even settled into a nice, lunging-size circle right around me.  He stopped, walked, and trotted on voice-command.  You would have thought I had a lunge line on the horse.  He only tried to turn around and go right a few times.  But the second I got behind him and popped the whip, he turned right back around and headed off to the left again.

We'll try again tomorrow.