When I was back in the states and livin' in Fl we had those traffic lights w/ the sensors for emergency vehicles. You could trigger greens w/ a strobe light gizmo at a certain pulse frequency for cars.

There was a write up in the paper once about how a certain intersection would always hem up at night and the DOT folks couldn't figure it out. Turns out the Radio shack close to the corner had strobe lights in the windows and it kept messing with the auto timer for the lights.

 

the traffic pads work like a hall effect sensor.
The metal in the car acting as a switch.
when the magnetic lines of force in the main circuit are "cut"
by the mass of metal in the car a different refernce signal goes back
to the light switching circuit.
Putting your kick stand down, brings the metal closer to the circuity
and could be just enough to trigger a sensitive circuit.
Will the magnet work consistently? no. but it will sometimes.
some lights even use a sonar type circuit, where you have to send a return signal
big enough (strong enough) to kick the circuit.
Having those styles I understand are illegal in some states.
May not be sonar per se but same basic principle.