I've seen the entire field glitched that way. At the time, my theory was that someone was doing it to gain invisibility or invulnerability, but it seems more likely someone is doing it just to be mean. (I don't know precisely how it is done, but haven't seen it last more than two hours on Abassa.)
http://i476.photobucket.com/albums/r...1_17-46-56.jpg