Ground movement of vehicles or aeroplanes in the vicinity of the aerials can cause this- I have seen it several times over the years. As to disconnecting itself, I think the autopilot would hang on for dear life. I do not think you would ever leave it in to the extent it would want to hold on. I have a wry smile to myself when people witter on about pilotless aeroplanes- examples like this and the BA 777 and many others, and faults 'not from the book' mean that although computers are a great help, for the unlimited future, human intervention is occasionally very necessary!