The issue

When MCMultiPart is installed alongside CTM (Connected Textures Mod) and vanilla textures are modified using the CTM .mcmeta, all the mcmultipart:multipart blocks turn invisible.

To reproduce

1. Instal the following mods:

CTM-MC1.12.2-1.0.2.31
MCMultiPart-2.5.3
* ResourceLoader-MC1.12.1-1.5.3
* EDX-Multipart-1.1.1

ResourceLoader-MC1.12.1-1.5.3 is there only to imitate the resource pack. The issue can be also reproduced without Resource Loader, using a resource pack.

EDX-Multipart-1.1.1 - bug can be reproduced with any other mod that uses MCMultiPart.

Multipart is still visible:

2. Change the texture of any vanilla Minecraft block, and add .mcmeta with CTM data to the texture.

You can use textures from this zip: resources.zip

• Extract the zip to the .minecraft folder, and reload textures.

After reloading the textures, the mcmultipart:multipart should turn invisible:

• Example .mcmeta
  The problem is with the extra "ctm" data:

{
    "animation": {
        "frametime": 8,
        "interpolate": true
    },
    "ctm": {
        "ctm_version": 1,
        "extra": {
            "light": 15
        }
    }
}