Steps to reproduce:
1. You have a subwiki with "Open for any user to join" membership type
2. Go to the subwiki's administration page
3. Click Users
4. Select "Only an admin can send invitations to join this wiki" and "Both global and local users are available in the wiki"
5. Click "Save"
6. Invite a user to that subwiki
7. Click "Invite"
8. Log in with that user (from 6)
9. Go to the "Wiki Index"
As the user, you are able to see just the "Home" (Main) wiki. You are not able to see the subwiki and you can't accept the invitation from Admin.