Currently there is a but in iOS8 custom transitions. When the custom transition is complete, i.e. [transitionContext completeTransition: YES] is called, UIWindow shows empty with no view hierarchy at all. That is seen as a black screen which is appearing instead of destination view controller’s view.
The workaround is to add all views back:
[[UIApplication sharedApplication].keyWindow addSubview: [destinationViewController].view];
Clean solution for now, probably will be fixed soon)