Nexuiz 2.3 introduced a lot of new features for mappers like tcGen, tcMod and deformVertex support. On the stock Nexuiz maps you can see this by the different moving teleporter/lava textures, the reflexions on glass in starship or warfare or the moving water on runningman and runier.
Some of the custom maps were 'bitten' by this as this introduces some small glitches. Like the jumppad on hydronex.. you can look through it, the lavatubes on lavaflag move now and look very strange, and the reflexive glass makes the overlapping parts on the shield near the flags VERY visible.
Please keep your eyes open and report bugs you see here so the map authors have a chance to fix it and improve the look on 2.3.