On the ground, he's the same. He will brace and rather go in circles all day than flex.
I have a very large hunch he's sore somewhere. I can speak from personal experience that when my back is out, there are sides my head won't turn because its just far too painful! But I'm loose enough to look the other way. Based on this, I'm betting he's hurting somewhere.
But the caveat is, I told his owner. Her response? Brown is not injured. I wrote about his stiffness and potential pain on the fb page we use as our main communication, after the one time he was behaving unlike himself completely.
My advice is generally shot down or ignored. Is there any way I can teouble-shoot/prove he is hurting? I doubt they will call the vet.