I have a strange app behavior: The App updates the GUI changes only after returning from the background to foreground. When launching, some GUI elements are also missing and appearing not until returning from background state. Any touch on buttons fires not until going to background and reentering foreground.
The problem is with iPhone, iPad and both simulators and with Xcode 5.2.1 up to 5.3. It appeared after deleting the app from the devices and resetting the simulator. Beforehand there was never a problem like this with this app.
When you can’t fix it, restore it: With version control i reverted the AppName.xcodeproj directory (Finder shows it like a file) and it fixed the problem.
Then Xcode offered me to “upgrade to latest recommended settings and perform project clean up” which “removes unnecessary build files”. I did that and also chose the “create snapshot option”. After that i had the same problem again.
The i reverted to that snapshot before the project settings update and it worked again.
Key take-away: “upgrading project to latest recommended settings” can have nasty side effects. Snapshots and version control are great stuff.
Further investigation showed that in Settings.bundle one missing Root.plist file was reason enough to kill my GUI. I had there Root~ipad.plist and Root–iphone.plist and thought the Root.plist is no longer needed. Looks like you need all three if you want separate plists for iPhone and iPad.