Q:

dismissViewControllerAnimated completion block is not called

I'm trying to dismiss a view controller like this:
[composeViewController dismissViewControllerAnimated:YES completion:^{

    NSLog(@"Hello"); // Never outputted
}];

The view controller is dismissed, but for some reason the completion block is never called.
I have never had any issues with completion block not being called with other view controllers.
This view controller is "special" though, because it's added as a child view controller (which I have not worked with previously in my app). Does this impose any side effects why the completion block is not called?
It's added like this: 
UIViewController *rootVC = [UIApplication sharedApplication].delegate.window.rootViewController;
[rootVC addChildViewController:self];
[rootVC.view addSubview:self.view];
[self didMoveToParentViewController:rootVC];

A:

Found out what the issue was: the 3rd party view controller I was using had overridden - (void)dismissViewControllerAnimated:(BOOL)flag completion:(void (^)(void))completion without actually calling completion()

