Retyring to post after first post crashed the forum:
I built a city. Have some people inside, Channeler outside. Someone (don't know who) moved into the city. Suddenly all the terrain becomes white. I move the channeler back home, and the result is in the linked screenshot: Half the world is white while the rest is normal, with a clear cut limit.
http://dl.dropbox.com/u/8046784/CutWorld.png
