Other people have posted similar problems as this, but mines a bit more specific :)
Basically using shape animation on a lattice to deform a joint works all well and good. BUT when you do the same using a cage deformer, the cage's points go negative and into the object - not smoothly between the shape keys.
Like the lattice, the cage is enveloped to the bones. But unlike the lattice I get the problem mentioned above. But if I simply parent the cage deformer to one of the bones instead of enveloping it like the lattice it works fine.
So basically is there a way to have a cage deformer envelped, and still have multiple shape keys on it working fine (more then 2 shape keys as I *think* it works fine with just 2). Or do I just have ta be happy with simply parenting it.
Hope I explained it properly, as I'm not to good with words ;)