Problem with replacment textures for Turbo Roundabouts

[mgb204]

I've been working on making the Turbo Roundabouts fit in with Paeng's Sandstone mod, but have run into a problem:



I decided to make the edges of the roundabouts that previously had transparent sections show the full sidewalk textures instead, partially to make it easier to create the new images and also because I never really liked the gaps they left behind. The red circles on the image show where for some reason these textures are not appearing as I would expect them too. I think the yellow circles should also show textures, but I'm less sure about those.

Is there some problem with changing the transparent sections in this way? Or can someone please advise me where I am going wrong or what to check?