Saving data downloaded off the inter webs

gistfile1.m

NSString *dataPath = [weakOperation tmpFilePath];

NSManagedObjectContext *context = [[NSManagedObjectContext alloc] initWithConcurrencyType:NSPrivateQueueConcurrencyType];
[context setParentContext:mainContext];
[context performBlock:^{
    NSError *findingError = nil;
    GOFeedItem *thisItem = (GOFeedItem *)[context existingObjectWithID:objectID error:&findingError];
    if(!thisItem){
        NSLog(@"Error finding item %@: %@", [feedItem title], [findingError userInfo]);
    }

    [thisItem setAudioData:[NSData dataWithContentsOfFile:dataPath]];
                
    NSError *savingError = nil;
    BOOL saved = [context save:&savingError];
    if(!saved){
        NSAssert(NO, @"FUCK!");
    }
    [context reset];
}];

According to Instruments, the child context is gone, but there's still a Malloc the size of that file there still alive.