Since my previous post I went to look at my removed, damaged sensor. I forcibly removed the "inner disc" which is the ultrasonic device. For the round sensors on the rear of the car, the device is about 1/4" deep, shaped like a cylinder with some fine wires out the back. That whole thing sits in a rubber sleeve the encapsulates the device, like a cup. What we see externally is like the rim of the cup, if you will.
It is obvious that the ultrasonic device needs to be decoupled from the mounting so that vibrations will not reflect back instantaneously, creating an extremely short "bounce" on the transmitted signal, thus a false positive.
If there is some hardened crud (that waxy buildup, bugs, dirt) mechanically bridging the rubber gap, it can cause false sensor readings.