The custom background image not appearing initially was not fixed in iOS7 GM or final, as far as I can tell. I see the same problem. It does seem to be an Apple bug; the private view Apple uses simply does not get a setNeedsDisplay call when it needs it on initial display. Doing anything to it which causes that call should fix it -- like pressing on it (which likely changes internal state so it calls setNeedsDisplay on itself), or bringing a modal up (which probably forces a redisplay of the entire view hierarchy on the next viewWillAppear: call).
Using leftBarItems instead also can work, but that may cause a lot of maintenance issues with existing code (some screens may have their own left items, expecting that when set back to nil they restore the original back item, for example).
As mentioned, ideally you would be able to change to a borderless look on iOS7, which means that the bug isn't really apparent (since there is no background image). For some iOS6/iOS7 transition situations though, that may be difficult (lots of screens, and/or the need to support older iOS versions for a while and too hard to have two looks implemented, and it doesn't look good borderless without other changes). If that's the case, the following patch should work:
@implementation UINavigationBar (BackButtonDisplayFix)
if ([UIDevice currentDevice].systemVersion.intValue >= 7)
* We first try to simply add an override version of didAddSubview: to the class. If it
* fails, that means that the class already has its own override implementation of the method
* (which we are expecting in this case), so use a method-swap version instead.
Method didAddMethod = class_getInstanceMethod(self, @selector(_displaybugfixsuper_didAddSubview:));
if (!class_addMethod(self, @selector(didAddSubview:),
Method existMethod = class_getInstanceMethod(self, @selector(didAddSubview:));
Method replacement = class_getInstanceMethod(self, @selector(_displaybugfix_didAddSubview:));
- (void)_displaybugfixsuper_didAddSubview:(UIView *)subview
- (void)_displaybugfix_didAddSubview:(UIView *)subview
[self _displaybugfix_didAddSubview:subview]; // calls the existing method
Note: UINavigationBar does currently have an override of the method in question, so I'd expect the method_exchangeImplementations style to be used. I just added the other stuff for safety in case Apple changes their code. We may go borderless ourselves, but I did find this approach worked as an option (until a more thorough UI uplift), at least.
Additional note: This bug appears to be fixed in iOS 7.1. So, the patch could be conditionalized to only install the methods if running >= 7.0 and < 7.1.
Thanks! I use this by subclassing the UINavigationBar and overriding the didAddSubview.