This is a case that should be handled by the port, though. It isn't happening in regular Quakespasm, for example. Anyway, I doubt it will do any harm to have a map fix in place for the time being. Shouldn't break if QSS ever receives an update for this, either.
BTW regarding z-fighting fixes: Apparently KillPixel had published a project called
Z-Fixed Quake back in 2013. According to his own accounts, he found and fixed almost 200 (!) cases of z-fighting in the original ID1 maps. Compared to that, the Quakespasm fixes are barely scratching the surface.
However, both KillPixel and this project have vanished and I gotta work with what I have. I still believe they fixed the most obvious and annoying glitches in the custom Quakespasm pak, so it's better to have that than nothing.