Model faces sometimes do not display if they are behind another face with a semi-transparent texture from the same model.

This issue:

• affects block and item models the same way.

• is still present when enabling the “Improved Transparency” options.

• does not seem related to cullfaces.

Without a texture pack, the only case where this applies seems to be slime blocks and honey blocks (MC-163098), as shown here:

Improved Transparency does not fix the issue as seen here:

However, it also affects items, as shown in this image, where I replaced the iron sword model with a custom model: