GKTurnBasedMatchmakerViewController works on iPad but not on iPhone - objective-c

Question

We've been having trouble with this issue for a while, and just cannot find the answer to it in the docs or online searches..
Our iOS game is based on OpenGL ES, and we are implementing GameCenter turn based gaming. The following code shows a matchmaking UI for creating a turn based match. This code works fine on my iPad 1 and iPad 3. However, it will not work on my iPhone 4S!
[ UPDATE: ] We were using a UIWindow at the top of the View hierarchy, with a GL View / Layer as a sub view. This obscured the new view when it was presented. I can see this window now by adding a UIView into the main window, and the GL view as a child of it. However, I still cannot interact with this view..
This code is from a .mm file where we mix C++ and Objective-C code.
// Configure the match making view, with our own delegate
GKTurnBasedMatchmakerViewController *mmvc =
[[GKTurnBasedMatchmakerViewController alloc]
initWithMatchRequest:request];
mmvc.showExistingMatches = YES;
// Uses our own delegate.
if(!g_pTurnBasedDelegate)
{
g_pTurnBasedDelegate = [[TurnBasedDelegate alloc] init];
}
mmvc.turnBasedMatchmakerDelegate = g_pTurnBasedDelegate;
// Get the main window's root controller and instruct it to show the match making delegate.
if(g_Env && g_Env->m_pWindow)
{
RefPtr<WindowIOS> pIOSWin = ref_static_cast<WindowIOS>(g_Env->m_pWindow);
UIWindow * pUIWin = (UIWindow *)pIOSWin->GetHandle();
UIViewController * pController = [pUIWin rootViewController];
if(pController)
{
g_pRootViewController = pController;
}
}
if(g_pRootViewController)
{
[g_pRootViewController presentViewController:mmvc animated:YES completion:nil];
}

Answer 1

Came back to this issue after a while. The problem was not with the Game Center controllers, but rather with how we were setting up our main application views. This just happened to work on iPad, but not on iPhone.
For our application, we need to initialize the whole view hierarchy in code instead of using a NIB / Storyboard.
Our old initialization steps were:
UIWindow init and make key.
UIWindow addView (our OpenGL window).
UIWindow addView (a touch responder UIView).
UIWindow rootViewController = [[ViewController alloc] init];
Adding our views directly to UIWindow would impede the functionality of View Controllers and cause undefined behavior on iPhone vs. iPad.
Our new initialization steps (to fix these issues if anyone is having them):
UIWindow init and make key.
UIWindow rootViewController = [[ViewController alloc] init];
rootViewController.view = [[GLAndTouchView alloc] init];
Hopefully, anyone stuck with the same problem will find this useful.