Upon leaving a world and reentering it, the roof will be engulfed in a giant, dark black, shadow (possibly caused by glowstone). Hovering near to the roof will fix a small area near to the player (until the player leaves and reenters the world, which causes the shadow again). Successfully recreated several times. Please see attached screenshots, (note how the shadow starts exactly where the glowstone starts). Please note that the ceiling is 2 blocks thick. The ceiling is made up of iron blocks with glowstone patterns. The issue is unaffected by the smooth lighting setting (off, minimum and maximum), the render quality (fast/fancy) setting, as well as the OpenGL and render distance settings. Issue also occurs when deloading and reloading the chunk(s).