iPhone dev Stupidity 83: you can't hijack the "back" button

From here and apple doc on backBarButtonItem: 

When this item is the back item of the navigation bar—when it is the next item below the top item—it may be represented as a back button on the navigation bar. Use this property to specify the back button. The target and action of the back bar button item you set should be nil. The default value is a bar button item displaying the navigation item’s title.