NSCalendarIdentifierIslamic is not predictable, so i think you will face some bug's here and there, I suggest to use NSCalendarIdentifierIslamicUmmAlQura instead.
For more about it check this answer: http://stackoverflow.com/a/8897011
Using NSCalendarIdentifierIslamic will lead some months to be duplicated and others to be vanished in your project.
And thank you for your amazing project.