I've got a role which is called _Visitor. I would like to be sure that this role has the absolute minimum capabilities, and when I examine the role through [Users>Role Capabilities], I see that there are a few capabilities which are currently enabled, but which I would like to disable. If I deselect these items, and press the "Save Changes" button, I receive confirmation that the changes have been saved, but they are still shown as being enabled, once the screen is refreshed.
However, if I perform the same basic steps with the "Author" role, I am able to edit the role, adding and deleting capabilities, with the correct results.
The _Visitor role is a role that I created some time ago. Is there some reason why I can edit one role, and not another?