-[UICollectionView reloadSections:] does not remove displaying cells from UICollectionView

ViewController.m

@import UIKit;

@interface ViewController : UIViewController <UICollectionViewDelegate, UICollectionViewDataSource>

@property (nonatomic, strong) UICollectionView *collectionView;

@end

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];

    UICollectionViewFlowLayout *layout = [[UICollectionViewFlowLayout alloc] init];
    layout.itemSize = CGSizeMake(self.view.bounds.size.width, 200);
    layout.minimumLineSpacing = 0;
    _collectionView = [[UICollectionView alloc] initWithFrame:self.view.bounds collectionViewLayout:layout];
    _collectionView.delegate = self;
    _collectionView.dataSource = self;
    [self.view addSubview:_collectionView];
    [_collectionView registerClass:[UICollectionViewCell class] forCellWithReuseIdentifier:@"cell"];

    dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(3 * NSEC_PER_SEC)), dispatch_get_main_queue(), ^{
        NSLog(@"reload");

        [self.collectionView reloadSections:[NSIndexSet indexSetWithIndex:0]];
        [self logCellCount];
    });
}

- (void)viewDidAppear:(BOOL)animated
{
    [super viewDidAppear:animated];
    [self logCellCount];
}

- (void)logCellCount
{
    int count = 0;
    for (UIView *view in self.collectionView.subviews) {
        if ([view isKindOfClass:[UICollectionViewCell class]]) {
            ++count;
        }
    }
    NSLog(@"cells: %d", count);
}

- (NSInteger)collectionView:(UICollectionView *)collectionView numberOfItemsInSection:(NSInteger)section
{
    return 5;
}

- (UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath
{
    UICollectionViewCell *cell = [collectionView dequeueReusableCellWithReuseIdentifier:@"cell" forIndexPath:indexPath];
    cell.contentView.backgroundColor = [UIColor colorWithRed:(arc4random_uniform(255) / 255.0)
                                                       green:(arc4random_uniform(255) / 255.0)
                                                        blue:(arc4random_uniform(255) / 255.0)
                                                       alpha:1];
    return cell;
}

@end