Okay, well after reading that, I've seen cases like this. The dog holds a leg up at certain speeds...but at other speeds seems perfectly normal. I tell the doc, they do X-rays, dog is totally fine...just an abormality.
Charlie, a chihuahua, holds his back left leg up every time he trots around...but he can sprint like hell on all fours, and walks slowly like a normal dog.
I'd still massage/bedrest often and see if it gradually helps.
Main thing is if you think he's in pain. If not, it might just be a wonky build on that leg.