Custom block models are incorrectly lit at low light levels

When using custom models for blocks (such as dripstone) the game will sometimes incorrectly render some faces of the model fully bright.

It happens when the block is on the edge between 1 and 0 block/sky light.

I don't think this should be classified as invalid because even tough it's only visible on non-vanilla block models this is a problem with the rendering engine itself rather than the texturepack.

Steps To Reproduce

1. Download and enable this resource pack

1. Go into the ocean

2. Find kelp

3. Observe the kelp becoming bright on the transition from 1 to 0 skylight

Alternatively

1. Download and enable the resource pack

1. Place down a torch

2. Dig a 13 block long tunnel away from the torch (as shown in attachment below)

3. Place a barrier block on the 12th block and a dripstone on top of it

4. Observe the bug

Expected Behavior

These blocks wouldn't be fully lit at very low light levels

Observed Behavior

They are.