Holes in Terrain?

On a terrain map I just put together recently, I noticed there is a hole in the surface, like a few of the squares were cut away. This is something I noticed also on two the maps that are on the demo, the waterworld map, and the bare map.

At first I though these might have been intentional, but I did not intend to have this in mine, so I wonder...is there any explanation for this, and has anyone else come across this? Its not particularly serious (not yet), and can be worked around if need be, but Iwas wondering if anyone else was aware of this.

Thanks