I found also a service manual online here: [http://www.csportal.panasonic-la.com/descargaspla/PLA/DIGITALES//CAMARAS//ALTO%20ZOOM/DMC-ZS20PU/DOCUMENTO/MANUAL%20DE%20SERVICIO//ZS20_Manual%20de%20Servicio.pdf]
When you look at page 58 you can see that the zoom function is combined with the movie recording button. You can even conclude that a bad contact in the "tele lo" (=zoom in slow) can result in a movie recording signal for the electronics.
So to clean that zoom button contact you can even move it a a while without switching on the camera. Especially the area from neutral to "zoom in" (= move to the right side) and back to neutral.
It helped with my device.
Let me know if it helps
BR, Peter