A video was released today showing what the classifier in Tesla's Autopilot sees, provided by an individual who hacked it. False positives galore:
It's just the radar data, not the camera based system. Further:
"Sometimes the circle is in place, where there's nothing present. It should be well known, that radar have problems with determining the elevation at which the object is located, so such readout can be caused by an object that is higher or lower on the image."
and
"Radar reports coordinates in 3D space and so the conversion to image space might not be super accurate at times"