I'm using the standard People Picker Navigation Controller to let users associate one of their contacts with one of my objects. It presents itself as a long list of ALL contacts. The back button (top left) says "Groups" but when clicked on it shows an empty screen...even when there are many Groups in the user's address book. I've read through the docs and can't seem to find how to populate the Groups area. Here's how I present the people picker. Fairly standard:

- (IBAction)showPicker:(id)sender {
    ABPeoplePickerNavigationController *picker = [[ABPeoplePickerNavigationController alloc] init];
    picker.peoplePickerDelegate = self;

    [self presentModalViewController:picker animated:YES];
    [picker release];
}

What am I missing?