The bug
I have a personal resource pack that, among other things, gives redstone wire its own dedicated model such that it fits its wireframe hitbox. The issue is that, despite specifying cullface on the edges as to hide texture planes that are never visible, this cullface does not work against other minecraft:redstone_wire blocks. It correctly works against solid opaque blocks, however.
How to reproduce
Download and apply the attached resource pack
Place redstone wire, preferably a straight line that points into the side of a block
Enter Spectator mode and inspect
Expected results
The edge faces obscured by the solid block and by other units of wire would not be rendered.
Actual results
The face pointing into the opaque block is indeed not rendered. However, the ones between units of wire, which is where most of these faces will be, are still rendered, even though they should not be.
Can confirm