glass/glasswindow001a

I am having a visibility issue in one of my maps that I can't get my head around. Basically certain items in the map appear to flicker when viewed, but only from a particular location. I recorded this to help demonstrate: The spinning item you see is a func_rotating, and wall around it that...

I was mapping for the 2016 spawnroom contest. I created a window as seen in the video, but when I fired an arrow at the right window, the left window turned black/dark. The glass material is glass/glasswindow001a on the other side and icarus/glasschrome003 on the other side. I checked, there...