iOS 6: How do I restrict some views to portrait and allow others to rotate?

I had the same problem and found a solution that works for me.
To make it work, it is not sufficient to implement - (NSUInteger)supportedInterfaceOrientations in your UINavigationController.
You also need to implement this method in your controller #3, which is the first one to be portrait-only after popping controller #4.
So, I have the following code in my UINavigationController:

- (BOOL)shouldAutorotate
{
    return YES;
}

- (NSUInteger)supportedInterfaceOrientations
{
    if (self.isLandscapeOK) {
        // for iPhone, you could also return UIInterfaceOrientationMaskAllButUpsideDown
        return UIInterfaceOrientationMaskAll;
    }
    return UIInterfaceOrientationMaskPortrait;
}

In view controller #3, add the following:

- (NSUInteger)supportedInterfaceOrientations
{
    return UIInterfaceOrientationMaskPortrait;
}

You don’t need to add anything to your view controllers #1, #2, and #4.
This works for me, I hope it will help you.