Just an FYI following Version 3.13.0 of JEI enabling listing of items with no models Quark is listing them for every wall it adds (displayed as broken textures/ Metadata :1)

Using Quark 57.

(Doesn't happen with Botania Walls)

I can second this with Quark 57, JEI 3.13.1.346 and Forge 12.18.2.2116. I tried looking through Quark's code, but I couldn't figure out why this was happening (and especially can't make sense of this being Quark's fault, seeing as it doesn't happen on JEI 3.12.8.323. Cross-reporting this to Mezz.

Chatted with Mezz about the issue, seems as though it's a broken model for sure on Quark's end :(

Yeah it's not JEI's end, just facilitated by JEI no longer hiding items/blocks with broken models, as mentioned above the feature was removed in version 3.13.0 which is why you couldn't see it in JEI 3.12.8.323.

On another note, cheating the broken texture blocks in/placing them leads to working textured walls being placed but when you break them they default to the normal meta 0 walls, I doubt the meta 1 walls are intended (I cant see any obvious indication of adding meta:1 walls in code) but my java knowledge is shit tier so what do I know :P

The meta:1 walls in vanilla are the mossy variant. I think it's just a simple mistake from copying the vanilla class that wasn't noticed because JEI hid it.