I ended up raising this with Developer Tech Support, and it looks like a bug. This is the response I got back from Apple:
The container view that the tab bar controller sets up to contain your view controller is not being resized to account for the interface being in landscape orientation. It's dimensions at the time your view controller is displayed are 768 (width) x 1024 (height).
The view hierarchy looks like this when the selected tab's view is displayed:
UIWindow
/* Navigation Controller */
UILayoutContainerView
UINavigationTransitionView
UIViewControllerWrapperView
/* Tab bar controller */
UILayoutContainerView
UITransitionView
UIViewControllerWrapperView <-- Incorrectly sized.
/* MyViewController */
MyViewController.view
The incorrect size of UIViewControllerWrapperView does not cause a display problem because subviews are still displayed even if they are outside their superview's bounds. However, event routing is much more strict. Events on the right quarter of the screen are never routed to your view controller's view because the hit test fails at the wrongly-sized UIViewControllerWrapperView where the event falls outside UIViewControllerWrapperView's bounds.
As a workaround, I subclassed UITabBarController, and added the following in viewWillAppear:
@implementation FixedIOS7TabBarController
- (void)viewWillAppear:(BOOL)animated {
[super viewWillAppear:animated];
// Fix the frame of the UIViewControllerWrapperView
self.selectedViewController.view.superview.frame = self.view.bounds;
}
@end
Hope that helps someone else....