I’ve spent far too long fighting with this bug today, mainly because Apple don’t appear to publish a list of the bugs they’ve fixed between iOS versions. And wow, their bug reporting tool is still styled after the 11 year old OSX Puma! There’s a design that says “we care about your bug reports”.
Anyway, here’s an example of a pathological Core Data database design that will crash iOS 5. It’s an obfuscated subset of the database I’m using in my current app:
Attempting to create an instance of “Entity3” and then set its “guid” attribute will crash iOS 5 every single time. What’s most annoying about this bug in the OS is that adding or removing an attribute or relationship anywhere in the object graph fixes the crash. The bug was silently fixed in iOS 6. There’s an example project here: