Sir Galahad & Gilbriar Abilene

So - we have to get Galahad mad about something (Dancer leaving, not being able to roll, dancer running) in order for him to canter on command. And he will only do it for a full circle in one direction. The other way I can get about 3 steps.

So now the question is why... is it a mental block? A physical sorness? Can he not see as well going in one direction? Or is he just being difficult?