Interesting. Have you tried calibrating it?
- Hold the windows button on your keyboard and press R (win+r)
- Type in joy.cpl and press enter.
- Then you just click on the controller, Properties, go into Settings tab and click the Calibrate button.
If that doesn't help, you could edit the .map file for the controller in a text editor, and try adding a slight deadzone on the axis used for walking, though that could be annoying when driving. You can add the deadzone so it only affects the walking controls.