Further update - removed all traces of Cover drivers and filters by installation and registry hacking. Removed drivers and downloaded fresh drivers. This seemed to fix things for a while. Then it came back. I've no turned off the illumination on the keyboard
- which again seemed to fix things for a while. It has occurred since, but seems less frequent (famous last words). Profoundly irritating and inconsistent. I have not managed to find way of consitently triggering it - or preventing it. It seems to appear more in the evening but isn't light dependent (thinking it might be pickup from the screen - varying brightness?). Temperature? Differing conductivity/capacitance of the fingers?