Thank you, Anthony! That fixes the problem instantly.
The switch in question is the GMCMode variable in the OpenNI\Drivers\PS1080.ini file. Uncomment the line which reads:
this turns GMC mode OFF. According to this article (https://github.com/OpenNI/OpenNI2/issues/81), GMC probably means Global Motion Compensation.
For comparison, the first image below is with GMCMode=1 (the default), whereas the second image is with GMCMode=0.
In this example, I have the Structure sensor looking down on a flat piece of cardboard. With the banding off it becomes possible to tell that the sensor is not quite perpendicular to the surface like I thought it was.