Hey Marc - yes you are right. And now I think I know when in my processing steps it happens. It's when I set the tonal range. It seems to clip when I set the darkest parts and the lightest parts. I try and recover during stretching but it doesnt reverse the clipping as far as I want it too. Next target I will go easy on the tonal range setting!
NB: Seems to be an issue only with the faint targets.