Multi-level navigation controller on left-hand side of UISplitView with a small twist.

Answer 1

Are you sure that MainViewController is a subclass of UINavigationController?

If you want to be able to push/pop controllers then the mainViewController should be a navigationController (or subclass) and then you would push controllers (e.g. TableViewControllers) onto that. You can see this structure in the default splitView project (open up IB and inspect the views).

Here is a decent tutorial on UISplitViewController: http://mobiforge.com/developing/story/developing-split-view-based-apps-ipad