Under the Geometry tab, selecting the machining boundary, help describes a couple of check boxes.
It looks like the second set of images in this screen grab are swapped, they don't match the first set and I think (correct me if I'm wrong) it's the first set that is correct.
The third pair of images in the pic is also wrong in that both images are exactly the same when they should be showing a difference. I think they are both showing the "disabled" condition.
Attachment 302100