The bug

Some blocks do not use directional opacity like slabs and stairs do. For example, placing a slab on this structure (Screenshot_225.png) in the way this stonecutter is placed would stop light from passing through. As of 18w46a, the stonecutter doesn't have any visible gaps in the model so the same logic should apply (Screenshot_226.png).

Affected blocks

^{Strikethrough implies that this case has been fixed}

• Stonecutter (Bottom)
• Lectern (Bottom)
• Daylight Sensor (Bottom)
• Carpet (Bottom)
• Enchantment Table (Bottom)
• End Portal Frame (Bottom)
• Shulker Box (Bottom and top) ¹
• Trapdoors (only the ones without holes in the texture) ^{2, 3}
  • Birch / Spruce / Dark Oak Trapdoors
• Wooden doors (only the ones without holes in the texture) ³ (see also MC-82773)
• Hopper (Top)
• Cauldron (Top)

¹ - Technically affects the sides as well, though it depends if the shulker box is open or not
² - Depends on which face the trapdoor is and if it is open or not
³ - Since only variants without hole in the texture would have to behave this way, it is questionable if this is really the desired behavior. In the end the behavior would be texture based and consistency between all variants would be lost.