The bug

Unlike ladders (MC-199237), vines (MC-199239), glow lichen (MC-212305) and other flat wall attached blocks, sculk vein blocks are not mirrored from behind as one would expect.

How to reproduce

1. Place sculk on a transparent block, e.g. barrier, glass
2. For comparison (expected behaviour), also place glow lichen or a similar block nearby for comparison
3. View the sculk vein from in front and behind

Expected results

The pixels seen from the front would be in the same positions when seen from behind.

Actual results

They appear on the other side when seen from behind, in contrast to other planes.

How to fix

A very easy model fix - just check the glow lichen model to see how it does it. I'd recommend just using a simple "flat plane" template model instead though - example forthcoming.