thank you ! I'm also clueless as to why this happens... but your models will come in handy!

bump

Edit mode: Element :element:
Location: Elements List
Function name: Batch Fast UV
Function icon: a yellow dye inside a minecart

Function action details:
Lets you apply Fast UV to either a face of your choice, or the 6 of them.
Lets you do these actions to all the elements currently selected ...

Edit mode: Element
Location: Element
Function name: Dye
Function icon: a stained glass pane

Function action details:
- On the 3D view, dyes those elements' faces whose UV map is 100% transparent texture
- On the 2D views, dyes the elements so they are not invisible anymore.

Right-click, then drag-drop

I disabled ambient occlusion and shading on the model and all the elements, respectively... Still getting black parts...
It's a really simple model, just a redstone wire line. See if you can give me a hand please? :)

https://i.imgur.com/RphCWkN.png

I attach to you my model (name is redstone_up ...