UITextView: Must I always resignFirstResponder?

Question

Must I always resignFirstResponder for a UITextView? Or, will this happen automatically when its view controller disappears?

I'm asking because I'm having an issue similar to iPhone Objective-C: Keyboard won't hide with resignFirstResponder, sometimes, where the keyboard stays up even when the nav controller pushes and pops other view controllers. The keyboard works, and when I hit done, it unfocuses the UITextView (i.e., the cursor disappears), but the keyboard stays up.

I never found out why this is happening, but maybe it's due to not doing resignFirstResponder before pushing another view controller, but I thought it was optional?