Mike, I had Gamma set to around 60% and Saturation pushed to nearly 90% to try and get some colour (maybe that has something to do with it too). I tried exposures at 1/30th sec and 1/20 sec so varied gain to suit from arond 30% to 20%.
Will have to have a go "in the dark" and see if the problem goes away... don't want it happening when that 9/10 seeing night come along
cheers,