What this looks like is a problem with your video card settings (or the card itself, but this is less likely). The quality of large textures is being degraded, which some people do to improve performance. What kind of a card do you have, and what's your operating system?
In Windows, the video card's OpenGL settings usually includes a slider that allows you to set a balance between performance and quality; moving it towards the "performance" end will have just this kind of effects.
Fingers said:
In Windows, the video card's OpenGL settings usually includes a slider that allows you to set a balance between performance and quality; moving it towards the "performance" end will have just this kind of effects.
Thanks, I had exactly this problem and your suggestion fixed it.