Why does adding 'dynamic' fix my bad access issues?

Question

I\'m having a strange issue that appeared with iOS 8 Beta 5 (this issue did not occur with previous versions).

I tried to create an empty project and try to replica

Answer 1

This is from the prerelease Swift / Objective-C interoperability documentation:

Implementing Core Data Managed Object Subclasses

Core Data provides the underlying storage and implementation of properties in subclasses of the NSManagedObject class. Add the @NSManaged attribute before each property definition in your managed object subclass that corresponds to an attribute or relationship in your Core Data model. Like the @dynamic attribute in Objective-C, the @NSManaged attribute informs the Swift compiler that the storage and implementation of a property will be provided at runtime. However, unlike @dynamic, the @NSManaged attribute is available only for Core Data support.

So, because of some of the Objective-C runtime features that Core Data uses under the covers, Swift properties need to be specially annotated.