I watched him again today...no problems. He backed up (I startled him with the hose) with no issues there, went nice and smooth.
Could his loose shoe have been the cause of the problem? I'm getting a farrier out this week sometime (if he has time...I really hope so, my Foxtrotters need to be trimmed and shod horridly).
I'm almost thinking about keeping Sam barefoot. I'll be talking to the farrier to see what he thinks. He's a pretty awesome guy, he did an amazing job on Loki's novice-farrier-ruined-hooves (he had no heel left or anything, it was nasty).