Alpha/Opacity not displaying through Visual Shader properly, even with "Depth prepass Alpha" enabled.

[Corruptinator]

Godot version

v4.0.1.stable.official [cacf499]

System information

Windows 10, Vulkan, Ryzen 3900, NVIDIA GTX 2080 SUPER

Issue description

I noticed that the Draw prepath Alpha for the Visual Shader isn't working correctly, for some reason it causes the object to fade/turn black when the float function is set to "0"...

This is through the Visual Shader Material:

While this is what was supposed to happen, albeit done with Spatial's "Depth Depth Mode" (done using the built-in spatial material):

Steps to reproduce

If anybody is interested to recreate this weird effect, just make a visual shader with a float parameter, and connect it to the "Alpha":

Attach the visual shader to any mesh, preferrably a mesh with fingers or claws. Then change the slider under the "Shader Parameters" in the material/material override section:

Make sure you enable the Draw prepath Alpha in the visual shader material as well:

Minimal reproduction project

Here is the project file to test it on. Had to use a different model instead of the one generated from Character Creator:
"Alpha_Test_Debug.zip

[Calinou]

@Corruptinator Please upload a minimal reproduction project to make this easier to troubleshoot.

[Corruptinator]

@Calinou Minimal reproduction project has been uploaded, had to use a different model cause the one I was using was generated from Character Creator 4, the one in the included project was generated from Makehuman just to avoid issues with content creation. But the setup should be the same:

Alpha_Test_Debug.zip

P.S. updated the instructions with more detail about activating the "Depth prepass Alpha" on the shader.