I tracked down where the original Kalman filter code came from and I'm pretty sure they did it incorrect after looking at the original source.  Their implementation didn't appear to work properly.  After seeing the original, I think they left out some key parts.

Plus can someone port code then give that ported code a GPL license and claim copyright on it without giving credit back to the author?

Anyways, I'll be knee deep in C code for a bit.