Sort master data results in NSFetchedResultsController

I have an entity Tagwith a string property tagName. I went to get all the objects in this Entity in NSFetchedResultsController, but I want the tag with tagName"Main" to be the first object. Here is what I am doing now:

 NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
    NSEntityDescription *entity = [NSEntityDescription 
                                   entityForName:@"Tag" inManagedObjectContext:appDelegate.managedObjectContext];

[fetchRequest setEntity:entity];

NSSortDescriptor *lastDescriptor2 =
[[[NSSortDescriptor alloc] initWithKey:@"tagName" ascending:NO comparator:^NSComparisonResult(NSString* tag1, NSString* tag2) {
    NSLog(@"compare");
    if ([tag1 isEqualToString:@"main"]) return NSOrderedAscending;
    if ([tag2 isEqualToString:@"main"]) return NSOrderedDescending;
    return [tag1 compare:tag2];
}] autorelease];  

[fetchRequest setSortDescriptors:[NSArray arrayWithObject:lastDescriptor2]];
NSFetchedResultsController *theFetchedResultsController = [[NSFetchedResultsController alloc] initWithFetchRequest:fetchRequest managedObjectContext:appDelegate.managedObjectContext sectionNameKeyPath:nil cacheName:nil];
self.fetchedResultsController = theFetchedResultsController;
self.fetchedResultsController.delegate=self;   

if (![[self fetchedResultsController] performFetch:&error]) {
    NSLog(@"Unresolved error %@, %@", error, [error userInfo]);
}

This code is called in my method viewDidLoadand is called only once. The first time it was called, for some reason, sortDescriptor is not used here - it just is not called (the operator is NSLogalso not displayed). My results are returned solely based on the value BOOLthat I specify for ascending- the block is ignored.

Tag MOC NSFetchedResultsController, sortDescriptor, NSLog(@"compare"), ! , , .

?