Vines using the "ctm_vertical" render type draw sideways on the back.
I haven't yet tested the other render types, but vanilla does NOT do this. Screenshots below show the issue ingame.

Assets used should they be the source of the issue:

{ "ctm": { "ctm_version": 1, "proxy": "block/ctm/vines" } }

Vine under "blocks/ctm"

{ "ctm": { "ctm_version": 1, "layer": "CUTOUT", "type": "ctm_vertical" } }

Issue in minecraft:models, apparently the X value being backwards is what makes that do that. How dare I want to turn the colourmap off, clearly.