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

The Bug:

Big dripleaves 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 big dripleaf.
2. Place blocks all around the big dripleaf.
3. Take note as to whether or not big dripleaves are rendered too dark when blocks are placed adjacent to them while smooth lighting is enabled.

Observed Behavior:

Big dripleaves are rendered too dark.

Expected Behavior:

Big dripleaves would not be rendered too dark.