Something different between OAStackView and UIStackView

[nerdycat]

• (void)viewDidLoad {
  [super viewDidLoad];

  UILabel *label1 = [UILabel new];
  UILabel *label2 = [UILabel new];
  label1.text = @"Some long text!!!";
  label2.text = @"ABC";

  OAStackView *sv = [[OAStackView alloc] initWithArrangedSubviews:@[label1, label2]];
  sv.translatesAutoresizingMaskIntoConstraints = NO;
  sv.axis = UILayoutConstraintAxisHorizontal;
  sv.alignment = OAStackViewAlignmentTop;
  sv.distribution = OAStackViewDistributionEqualSpacing;

  [self.view addSubview:sv];

  [sv.topAnchor constraintEqualToAnchor:self.view.topAnchor constant:50].active = YES;
  [sv.leftAnchor constraintEqualToAnchor:self.view.leftAnchor constant:10].active = YES;
  [sv.rightAnchor constraintEqualToAnchor:self.view.rightAnchor constant:-10].active = YES;

  UILabel *label3 = [UILabel new];
  UILabel *label4 = [UILabel new];
  label3.text = @"Some long text!!!";
  label4.text = @"ABC";

  UIStackView *sv2 = [[UIStackView alloc] initWithArrangedSubviews:@[label3, label4]];
  sv2.translatesAutoresizingMaskIntoConstraints = NO;
  sv2.axis = UILayoutConstraintAxisHorizontal;
  sv2.alignment = OAStackViewAlignmentTop;
  sv2.distribution = OAStackViewDistributionEqualSpacing;

  [self.view addSubview:sv2];

  [sv2.topAnchor constraintEqualToAnchor:sv.bottomAnchor constant:50].active = YES;
  [sv2.leftAnchor constraintEqualToAnchor:self.view.leftAnchor constant:10].active = YES;
  [sv2.rightAnchor constraintEqualToAnchor:self.view.rightAnchor constant:-10].active = YES;
  }

The codes are very similar, one for OAStackView, one for UIStackView. The result is different, the label1 get clipped and label3 is fine.