I believe the activation of Navipanel has nothing to do with magnetism. It is the connection with the mains that triggers the app.
Why do I think so? Because I ordered the 'Motorola mini usb to micro usb adapter'. When I connected this adapter to the 12 V car charger of my old HD, the navi-app on my HD2 came on, the screen tilted 90 degrees and the speakerphone switched on. So I got rid of that Motorola adapter in the car
Other adapters don't have this behavior.
So believe the feature has to do with the wiring in the connector.