Back button not appearing on UINavigationController - can't debug - objective-c

Question

The back button on a navigation controller is sometimes not appearing. Note that sometimes it does, so there is probably something else going on in som code elsewhere, but I have tried to debug this in every way I can think, and nothing seems to work.
The code for pushing the view controller is as follows (pretty standard):
CommentsTableViewController *vc = [[[CommentsTableViewController alloc] init] autorelease];
vc.puzzleID = self.puzzleModel.puzzleID;
[self.navigationController pushViewController:vc animated:YES];
To debug this problem, I have put the following code in the CommentsTableViewController in viewWillAppear and viewDidAppear (except I only register as an observer once):
self.navigationItem.hidesBackButton = NO;
[self.navigationItem addObserver:self forKeyPath:#"backBarButtonItem" options:(NSKeyValueObservingOptionNew | NSKeyValueObservingOptionInitial) context:nil];
self.navigationItem.backBarButtonItem.title = #"Tactic";
NSArray *viewControllerArray = [self.navigationController viewControllers];
int parentViewControllerIndex = [viewControllerArray count] - 2;
[[viewControllerArray objectAtIndex:parentViewControllerIndex] setTitle:#"Tactic"];
None of this seems to help. Putting breakpoints in, it seems like the view controller above me in the hierarchy has a title (#"Tactic") and hidesBackButton is already NO. The backBarButtonItem property is nil and is always nil, though I think this is expected behavior even when you do have a backBarButtonItem?
EDIT: In the parent controller, I am setting hidesBackBackButton to YES at first, and then later (before I push on the next controller), setting it back to NO. When I remove these lines, the new view controller has a back button. Why would the navigation item of one view controller affect the navigation item of the next?
Any suggestions or ideas are welcome. Thanks a lot.

Answer 1

Perhaps you might solve the problem debugging it better.You assumed that the button that leads you back is this:
self.navigationItem.backBarButtonItem.title = #"Tactic";
But that's nil, if you want to find that button look in the navigation controller's navigation bar:
NSLog(#"%#",self.navigationController.navigationBar.topItem);
I don't see a reason why your code isn't working, and you also don't need to do this:
self.navigationItem.hidesBackButton = NO;
Try this instead:
self.navigationController.navigationBar.topItem.hidesBackButton = NO;
Anyway this works for me even if I don't set it to NO.
If this doesn't solve the problem it should help at least debugging it, and if you still have that problem post in the comments, and say what does that NSLog() print.

Answer 2

Ok. I've worked it out. I have no idea why this makes a difference, but it does.
In the same run loop where I was calling hidesBackButton, I was also calling:
[self.view addSubview:self.chessBoardViewController.view];
This seemed to be the line that was screwing up the navigationBar somehow. If I remove this line, it works perfectly. So the solution I found was replacing this line with:
[self.view performSelector:#selector(addSubview:) withObject:self.chessBoardViewController.view afterDelay:0];
I dont' know why this worked, so if anyone has any insights on what might be happening, please comment.