Pumpkin bottom texture can't be made different than top

I am creating a resource pack and I want to change the bottom texture of the pumpkins. However, the pumpkin bottom texture uses the top texture.

Steps to reproduce:

1. Create a resource pack or download it bellow and skip to step 4.
2. Create a texture to the pumpkin bottom in "textures/blocks" file and then a identifier to it in "terrain_texture.json" (for example, "pumpkin_bottom").
3. Change the bottom texture identifier of the pumpkin in "blocks.json".
4. Load it in Minecraft.

Expected Results:

The pumpkin bottom texture is different from the top texture.

Observed Results:

The pumpkin bottom texture is the same from the top texture. It seems that the bottom is using the top texture. This also happens to the "lit_pumpkin" (jack o'lantern) and to the "carved_pumpkin".

 

Below, you can see parts of the code (in "terrain_texture.json" and "blocks.json") and also the resource pack.