Can't resign first responder in UITextView

If you place a UITextView within a UITableViewCell that's being shown
modally with a presentation style of UIModalPresentationPageSheet, you
might notice that you can't actually resignFirstResponder on the text
view. It appears this is by design, even though it's annoying
(especially if you're presenting with a navigation controller where
the keyboard makes no sense on certain screens in the navigation
hierarchy).

You can adjust the presentation style (FormSheet or PageSheet) and
you'll notice that the keyboard gets dismissed as expected. The user
can always hide the keyboard until the modal view is dismissed if you
need to keep the FormSheet style.