It was the stride. That's what I was missing. I set the vertex buffer somewhere else in my code, and didn't even notice I hadn't changed the stride to reflect the skinned vertex.

Yeah, my journal entry assumes an equivalence between "programming" and "debugging." It isn't intended to imply you're new to programming. I should change that to emphasize familiarity with debugging techniques. Unfortunately, it seems that techniques to debug programs (which experienced programmers know will have to be done sometime) aren't taught as well (if at all,) as are programming techniques. Also, I acknowledge you've been "debugging." I'm suggesting a more structured approach.

I took a class for debugging. Most of the information taught were things I had learn myself.

Thanks for the help, now I can try to implement skinned meshes! Wish me luck!