@gmcrozier This glitch appears to occur only on specific lots. I'm currently going through Willow Creek and finding some that have it and some that don't. If you have a chance, could you check Oasis Springs? It's pretty quick to recreate. Just bulldoze the lot, paint the entire lot with flooring and then draw random fountains and/or pools around the lot. If the lot has the glitch, it will change some of the flooring back to grass, visually, and will not let you change those tiles.
Edit: If you could screen shot each lot with the issue, it would be helpful. And if you don't have time to do this, don't worry about it; I'll do it when I get a chance.