I'm going through the motions of optimizing a nearly finished map and right now I've been isolating with areaportals. I had to go through a few cycles of leak fixing that made sense until this. Basically, I have windows on the ceiling of a room. When I changed their texture to something opaque, like metal, and compiled, the room was sealed, perfect! But when I applied any translucent glass texture, on either face (in this case the texture is 'glasswindow001a') and compiled, I get a leak error. I checked the pointfile, and the line draws directly THROUGH the brush. Like I said, with the opaque texture it's leak free and obviously it's a world brush. Can you just NOT use translucent textures to seal areas? I mean I guess it's not that crazy considering you're seeing what's beyond it, and i could just slap an area portal behind it, but still pretty odd since I've never heard anyone mention it in discussions or tutorials.