This may not be related to your troubles, but I thought I would share something that causes this type of problem for me frequently, just in case.
Sometimes when doing funky things with a tspline, the tangent controls get unlinked from their vertices's. This can make a tspline body look just fine in box mode, but be completely messed up in smooth mode. You can tell if this has happened by going into edit form and selecting the vertices's selection filter. Un-less you've moved them on purpose, all the tangent control points should be green (you may need to change the opacity of the body to see all of them). If any of them are red, then they have become unlinked. This video demonstrates this pretty good, and shows the command to fix it.
http://forums.autodesk.com/t5/post-your-tips-and-tutorials/stuff-you-need-to-know-tangent-handles/m-...
