core data crash occurs on line 26: 2013-12-20 17:38:48.435 CoreDataCrash[23059:70b] *** Terminating app due to uncaught exception 'NSObjectInaccessibleException', reason: 'CoreData could not fulfill a fault for '0xcf61c00 <x-coredata://E61319FE-C903-4281-A90D-A0C46FE7F816/Widget/p7>''

gistfile1.m

self.parentMoc = [[NSManagedObjectContext alloc] initWithConcurrencyType:NSPrivateQueueConcurrencyType];
self.parentMoc.persistentStoreCoordinator = self.persistentStoreCoordinator;

self.childMoc = [[NSManagedObjectContext alloc] initWithConcurrencyType:NSMainQueueConcurrencyType];
self.childMoc.parentContext = self.parentMoc;

[self.parentMoc performBlock:^{
    NSEntityDescription *desc = [NSEntityDescription entityForName:@"Widget" inManagedObjectContext:self.parentMoc];
    Widget *w =[[Widget alloc] initWithEntity:desc insertIntoManagedObjectContext:self.parentMoc];
    w.name = @"derp";
    [self.parentMoc save:nil];
    NSManagedObjectID *objectId = w.objectID;

    [self.childMoc performBlock:^{
        NSError *childExistingObjectError;
        Widget *myW = (Widget *)[self.childMoc existingObjectWithID:objectId error:&childExistingObjectError];
        myW.name = @"herp";

        [self.parentMoc performBlock:^{
            [self.parentMoc deleteObject:w];
            [self.parentMoc save:nil];

            [self.childMoc performBlock:^{
                NSError *childSaveError;
                @try {
                    [self.childMoc save:&childSaveError]; // CRASHES
                } @catch (NSException *exception) {
                    NSLog(@"%@", exception); // NEVER CALLED
                } @finally {
                    NSLog(@"finally?"); // NEVER CALLED
                }
            }];
        }];
    }];
}];