I had a bit of a break for the holiday which was very, very needed. My brain was starting to freeze up.
Now that I’ve been back, I’m hitting the animation issue again, and I’ve tested a variety of theories about the problem. I think I’ve narrowed it down (in order of likelihood) to an error in how I’m working with the joint constraints. I’m probably asking too much of certain joints that aren’t capable of delivering the motion in SL.
This will require a little reskinning and weighting, but not much, I think. I’m working on that now and should be able to test it in a day or so.
When I have more concrete information about what I did to fix it, I’ll explain it more on the blog in case anyone else has the same issue.
Fiona Branagh's Blog 
Fiona Branagh
February 27, 2013 at 5:15 pm
While I was able to narrow down the problem to a likely issue and work around it, I finally learned WHY the joints worked as they do. I didn’t know that the following bones are completely ignored in the BVH upload to SL: mHipRight, mHipLeft, mToeRight, mToeLeft, mEyeRight, mEyeLeft, mSkull.
I knew some of them were, but didn’t have the complete list. I hope this helps others who are trying to learn the pipeline to SL on their own like I am.