CSG Problem

[macaronifeet]

I'm currently developing a map and for some reason whenever I use the CSG add or subtract buttons this happens:

Before:
http://i304.photobucket.com/albums/nn189/Knight_Industries/UDK1.jpg

After:
http://i304.photobucket.com/albums/nn189/Knight_Industries/UDK2.jpg

This doesn't occur on older saves of the map. Does anyone know how to fix this problem?