Steps to reproduce:
-Create an organization with an empty page and add the Wiki portlet
In Wiki portlet: Configuration>Permissions
Available roles include Organization member, Organization content reviewer, etc.
-On Scope tab, change value to "Current Page" (Or any other value besides "Default"...) and click "Save"
-Return to permissions tab
Aforementioned roles are no longer listed - instead, their Community counterparts are available
I found several similar issues present in JIRA, some of which are closed, and many are certainly related to this problem. However, this report concerns scoping and permissions in general and not in the context of e.g. Staging or a particular portlet.