Transparent textures don't render correctly on FOFs

If you have a transparent (read: invisible pixels, not translucent) texture as the main texture of an FOF, while drawing each column of pixels, the game will skip the transparent ones, but only until it finds an opaque pixel. From then on, it fills the remaining transparent pixels in the column with garbage.

Using a transparent main texture on a Sides Only FOF is a common trick to have a grassy border on an FOF, but this texture (WEEDWALL) exposes the problem that the more common texture, GFZGRASS, didn't.

Only textures with a single vertical column of pixels starting from bottom-up will draw correctly. This is why the trick in GFZ works.