I would agree that it would make sense that it uses the GPS at startup. What really makes me wounder is why is can be 100' +/- off sometimes at startup. Once a 3d fix is acquired it can get the elevation.

I have read a lot of posts on http://forums.motionbased.com/smf/index.php?board=86.0 where folks waited 30 miunutes and the elevation was still off.

As you and I have both said, some sort of manual calibration method would solve.