Just recently started using world edit to clear out large swaths of blocks and noticed that when I started making a tunnel near the surface, a large "burnmark"-like stain or shadow appears on the surface blocks above where the tunnel happens to be. Below are some screen shots, illustrating the problem.
So here is the tunnel at 'ground level'...

And here are some aerial shots of the burn mark above where the tunnel is located...



Any ideas for investigation?




