Is this still a problem?

Yes, just tried this map.

Can you indicate which grid (from bottom left)? I better fix this issue before I update the map tomorrow. Thank you very much.

I noticed one area around the center, but it's kinda fuzzy. Look around x & y 0 (holding C). Haven't checked elsewhere.

Ive found the worst area is around the central coal fields (NE of the lake), though I have found that if i select the level terrain (average) tool and give it a once over, it is fine and fixes any issues

I have noticed same issue on other maps also. i'm not sure that this has anything to do with it, on close inspection of the area where it was happening on another map the height was barely above sea level and some water was clipping through some spots, but it was barely noticeable. After flattening the terrain the issue in that spot disappeared. I may be completely wrong, but i though I share my experience, hope it helps.

If you go into your save folder and delete the file quadtree.dta it will fix mouse cursor not moving on maps.

The glithy areas can be fixed by using the terrain tool on them.