Selection of contact groups is not sticky. (Resets)
IOS 9.0.1
If you select only some groups to be displayed in the contact list, it is not sticky. It resets after "killing" the addressbook and restart the app.
Confirmed as a bug? (Reported her as well -> http://forums.macrumors.com/threads/contact-group-selections-not-sticking.191724 8/ )