The bug

If assigned a 3D model (made of cuboids, rather than only planes), chains will not have any of their faces culled against other chain blocks even if those faces are occluded. Such faces are correctly culled against solid blocks, however.

How to reproduce

1. Download and apply the attached resource pack
2. Place at least two cacti atop each other
3. Place at least two chains atop each other
4. Enter Spectator mode
5. Observe the cactus and chain from beneath

Expected results

For both the cactus and the chain, the face against the ground would be culled, as would the face between the two constituent blocks.

Actual results

The bottom face is culled against the ground for both blocks, but only the cactus has the face between the two constituent blocks culled.