OG role can't configure member roles

I have created a role named "Content OG Admin". This role has the permissions "Configure Member Roles".

When I assign the role within a group, the user has a "Configure Member Roles" tab (arrived at via the "X Members" menu item), but when they click the tab, the are told they do not have permission to see the page.

BTW, if I assign the role outside the group, the user can configure member roles in any group. This is, of course, not what I want, but at least it shows that the permission is working in a different context. Thanks.