Trapdoors are rendered too dark when blocks are placed adjacent to them while smooth lighting is enabled

The Bug:

Trapdoors are rendered too dark when blocks are placed adjacent to them while smooth lighting is enabled.

Steps to Reproduce:

1. Enable smooth lighting and place down a trapdoor.
2. Place blocks all around the trapdoor.
3. Take note as to whether or not trapdoors are rendered too dark when blocks are placed adjacent to them while smooth lighting is enabled.

Observed Behavior:

Trapdoors are rendered too dark.

Expected Behavior:

Trapdoors would not be rendered too dark.