I have a custom container view controller: `ContainerVC`. Its job is to present one of two content view controllers: `ContentPortraitVC` or `ContentLandscapeVC`, depending on the current orientation (though it doesn't matter why the container chooses its view, I presume). `ContentPortraitVC`, at some point pops up `ContentModalDetailVC`.

So there are two different methods of displaying new content at work here:

* the parent-and-child relationship (instigated via `addChildViewController` and removed via `removeFromParentViewController`),
* the presenting-and-presented relationship (instigated via `presentViewController` and removed via `dismissViewController`).

If the `ContainerVC` adds the `ContentPortraitVC`, which then presents the `ContentModalDetailVC`, and then the `ContainerVC` decides to switch to the `ContentLandscapeVC`, the `ContentModalDetailVC` stays visible (why is it not removed when its parent is removed?) 

But then, when the `ContentPortraitVC` is asked to remove the `ContentModalDetailVC`, nothing happens. The modal display stays put. What is going on?