Hehe, it might be because of my lack of mapping experience but I always use common/caulk for that. It seems that sometimes it gives a graphical bug though, as if you look out of the bounds of level (dont know how the 'effect' is called but it keep overdrawing what has previously been drawn on the place of the caulk part) .. Anyway you've solved it Smiley Im going to check out the shaders too..
Its due to the vising process, as caulk gets calculated & is viewed as a solid object that you cant see through. However if you changed it to "detail brush" the problem should not happen.
Hmm would it then work to use caulks as invisible walls?
I should learn more about these detail brushes, have never used them