The fire_0/fire_1 block texture is used as part of the fireballs that are shot by blazes and ghasts. However, unlike with other on-fire entities, the fire texture is not rendered in the same place as the fireball, but instead slightly infront. This causes the fireball texture to be entirely obscured, and is inconsistent with other on-fire entities as they render the fire texture in the same place as themselves.
Take note of the position of the fireball texture in the screenshots compared to the fire texture, and how the fireball trails behind it.
Expected Result: Fire overlay texture is rendered in the same place as the fireball, causing the fireball texture to render infront
Observed Result: Fire overlay texture is rendered slightly infront, causing the fireball texture to be entirely obscured
Image that best shows the issue, note how the fireball is significantly behind the fire texture.