Hi,
I recently ran into the same problem with a Saitek throttle quadrant: the right-most lever (mixture) responded also like a yes/no switch when the lever was around mid course.
I brought the throttle back to the store where they tested it and it worked perfectly.
Later, in Windows calibration panels, I found that my null zone cursor was correctly set symmetrically around the middle, but the other pair of cursors defining maximum travel (not sensitivity) were located just next to the null zone. All the four cursors were placed as close as possible to the middle point of their ranges. The lever worked perfectly when I dragged the travel sensors back to maximum deflection.
I hope I'm clear, but there was a simple fix. Don't know if this helps macwino, but maybe someone else...
Cheers,
Vincent