There is a square around character on the ground, lines like 1px size, and moves with character. It is not always visible probably because of terrain, angle of camera and so on, so sometimes you see just a line, sometimes 2 and sometimes all.
I assume it is related with generating grass and other terrain details area (note on the last pic that area inside square is more sharp and detailed than outside). It is not a problem, just a rather minor annoyance on the screen. If its borders could be completely invisible, would be fine.
Only change in setting is vg_fov with value 70.
Kubuntu 11.10 x64
Nvidia driver: 280.13
Nvidia GTX 460 (768)
4gb ram, i5
This thread belongs to Linux support, my bad. Please move it there.