ViewWillAppear is not getting called on Device

I recently made a change in my application to move some dynamic layout calls from ViewDidLoad() to ViewWillAppear (bool animated). On the simulator, this has worked great. It was exactly the change that was needed. But, for some reason, when I try to run the same code on my iPhone, ViewWillAppear is not getting called. I've tried setting a debug point on the first line of code in the method. It triggers in the simulator, but not on the device. I'm using the basic UINavigationController and calling

this.NavigationController.PushViewController(vc,true);

to load the screen. Is this a bug with Xamarin, or is something else going wrong?