The iPhone keyboard overlaps the tab bar by default, but it also behaves like a subview of the view that is inside the tab bar; for example, if it is open inside a UINavigationController-governed view, and you navigate Back, the keyboard slides away along with the view.
How do I get a UIPickerView to behave like this? It's layered behind the tab bar, so merely changing the position does nothing useful; I can attach it directly to the tab bar's view, but then it doesn't go away automatically with the view inside the UINavigationController.