Both the end-link of the thumb, and the link for the head are missing in the modifier, unable to have their envelopes or vertex assignments edited, though they are apparently listed as being part of the rig.
If worst comes to worst, I'll likely just do away with the biped bones altogether, hack apart pieces of a clone of the character model and use those for a bones system, but I'd rather not do that because as it is, the rig is able to handle the twist of the forearm perfectly without any editing on my part, and using a different system would likely force me to spend countless hours adjusting envelopes until the forearm twist works properly again.
The weird thing about these biped bones is that even after they've been snapshotted, when they are used in a rig, they're links take the exact same shapes. Even the links for the hand are divided by fingers the same way it did when it was part of a biped based system. I don't begin to understand that...
Does anyone understand why I'm having this link vanishing act?