I'm having this issue and I have not found an answer through search.
I have both a Spacepilot Pro and Space Navigator.
When I am moving around an object in either MAYA/MAX, I notice that the roll (twisting the controller) gradually slows down when I tilt to be in line with the horizon, until it gradually switches direction...
Eg: If I am orbiting a car, and I am dropping the height of my orbit until the ground plan is parallel to my view, then the roll has virtually stopped working, and then if I continue to roll... until the ground plane is now viewed from underside.. the roll has inverted its direction.
Please help as this is making the products unusable for me
Thanks