I was in a huge open space and couldn't summon him so I shouted his name at my feet and he appeared on top of me. I think the shout is a bit random in where it lands or how it works.
i'm pretty sure it's just bugged. He is, and currently still is, infinitely flying in Dayspring Canyon, for me. If I summon him out of Dayspring Canyon, aiming at the sky, he appears there, attacking anything near by, just like Odahving. If I aim at the ground, he appears there. This seems to be the same thing for me on every single character, however. I'm still leaning towards a bug.