Not sure I understand what the bug is - can you clarify? The image looks fairly normal to me
Hmmmmm that's a really weird bug. It looks like it's loading the wrong sprite files for some reason.
Have you tried any other mods that add a lot of sprites like Hardmode and do they cause similar problems?
If you go to the "mods/NTTE/sprites/areas/Coast/Decals/" folder does it look like this?