[Therion] Colour fill problems

Hi Can I fix the patch of white on the right, inside? The wall has the tick on the air side, and it is all in one scrap. I have tried to break the wall down into small pieces, but it gives exactly the same result? There are no Warning: scrap outline intersects itself in scrap (well not in any of the scraps that make up that area of cave) Which seems to be the closest thing I can find in the thbook or wiki Any other ideas? thanks Andrew