Falling through terrain...

I found a very annoying thing...looks like a bug. When I start the mission editor and create a fractal terrain for example, my character starts falling through the terrain. Bringing the camera above the terrain shows "holes" all over the terrain and when I place my character at camera position, it gets below the terrain again...is there anything I can do?

Found another possible bug...when trying to create a waterblock I get an error:

NetObject::onCameraScopeQuery: object marked both ghostable and as ghost