Spoiler: ScreenshotThe screenshot pretty much explains it. The top sidedef (the center area of the top trimming right above the pillar) uses "light = 32" to offset the light level to match the surrounding trim, while keeping the sector a lower light level.
It works fine in software, but it's screwed in OpenGL - It seems the renderer is ignoring the light statement for upper and lower textures and only applying the light offset to the middle texture only. Since the trim is an upper texture, it retains the sector's light level.
