Title & screenshots say it all.
Also I can't fix this with a simple model change, as all items apparently, by default, use a model called 'generated' which, since it is not present as a file, I assume is hard-coded. It just seems to be missing a few faces.
Only visible on torches and redstone torches at the moment.
It isn't an issue with my textures, as I can clearly see the 2D item and the front of the 3D item are both completely fine, and my pack does not modify the models at all.