That texture is a so-called tiling texture where every 240x240 pixels (divided by HLBSP), the texture changes. In naming conventions, they are similar to animated textures.
You're apparently missing the first texture in the series, either in the WAD itself, or the wrong texture is used in the map. If you don't want the "interchanging tiles" effect, you can rip the texture and place it in a separate WAD with a different name. :)