UILabel文字与父视图边框出现混合渲染问题求助

我有一个不透明的UIView（TagView），内部包含白色不透明的UILabel，将其作为带边框视图（MyControl）的子视图显示时，发现UILabel的文字中出现了父视图的边框颜色（如字母"y"与边框颜色混合）。尝试让父视图其他内容重叠显示时渲染正常，仅边框存在此问题，推测是父视图边框与UILabel文字的图层渲染混合逻辑异常。

以下是相关代码：

import UIKit
import PlaygroundSupport

enum TagType {
    case minimal
    case rounded
    case circle
}

class TagView: UIView {
    var tagType: TagType = .rounded { didSet { updateUI() }}
    var isSelected = false { didSet { updateUI() }}

    private(set) lazy var label: UILabel = {
        let label = UILabel()
        label.textAlignment = .center
        label.translatesAutoresizingMaskIntoConstraints = false
        label.clipsToBounds = true
        label.font = .systemFont(ofSize: 15, weight: .semibold)
        return label
    }()
    
    override init(frame: CGRect) {
        super.init(frame: frame)
        setup()
    }
    
    required init?(coder: NSCoder) {
        super.init(coder: coder)
        setup()
    }
    
    private var leadingLabelAnchor: NSLayoutConstraint?
    private var trailingLabelAnchor: NSLayoutConstraint?
    
    private var topLabelAnchor: NSLayoutConstraint?
    private var bottomLabelAnchor: NSLayoutConstraint?

    var constantValue: CGFloat {
        tagType == .circle ? 12 : 8
    }
    
    var verticalInsetTop: CGFloat {
        tagType == .minimal ? 3 : 5
    }
    
    var verticalInsetBottom: CGFloat {
        tagType == .minimal ? 3 : 7
    }

    private func setup() {
        clipsToBounds = true
        addSubview(label)
        leadingLabelAnchor = label.leadingAnchor.constraint(equalTo: leadingAnchor, constant: constantValue)
        trailingLabelAnchor = label.trailingAnchor.constraint(equalTo: trailingAnchor, constant: -constantValue)
        leadingLabelAnchor?.priority = .defaultHigh
        leadingLabelAnchor?.isActive = true
        trailingLabelAnchor?.priority = .defaultHigh
        trailingLabelAnchor?.isActive = true
        
        topLabelAnchor = label.topAnchor.constraint(equalTo: topAnchor, constant: verticalInsetTop)
        topLabelAnchor?.isActive = true
        
        bottomLabelAnchor = label.bottomAnchor.constraint(equalTo: bottomAnchor, constant: -verticalInsetBottom)
        bottomLabelAnchor?.isActive = true
        
        layer.borderColor = UIColor.blue.cgColor
        layer.borderWidth = 1
        updateUI()
    }
    
    override func layoutSubviews() {
        super.layoutSubviews()
        updateUI()
    }
    
    private func updateUI() {
        leadingLabelAnchor?.constant = constantValue
        trailingLabelAnchor?.constant = -constantValue
        
        topLabelAnchor?.constant = verticalInsetTop
        bottomLabelAnchor?.constant = -verticalInsetBottom
        
        backgroundColor = isSelected ? .blue : .clear
        label.backgroundColor = backgroundColor
        label.textColor = isSelected ? .white : .blue
        
        switch tagType {
        case .minimal:
            layer.cornerRadius = 10
        case .rounded:
            layer.cornerRadius = 12
        case .circle:
            layer.cornerRadius = bounds.height / 2
        }
    }

    func configure(with text: String) {
        label.text = text
    }
}

final class MyControl: UIControl {
    private lazy var tagView: TagView = {
        let view = TagView()
        return view
    }()
    
    override init(frame: CGRect) {
        super.init(frame: frame)
        setup()
    }
    
    required init?(coder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }
    
    private func setup() {
        tagView.translatesAutoresizingMaskIntoConstraints = false
        tagView.isSelected = true
        backgroundColor = .clear
        layer.cornerRadius = 10
        layer.borderWidth = 2
        layer.borderColor = UIColor.blue.cgColor
        
        addSubview(tagView)
        
        NSLayoutConstraint.activate(
            [
                tagView.leadingAnchor.constraint(equalTo: leadingAnchor, constant: 8),
                tagView.topAnchor.constraint(equalTo: topAnchor, constant: -16)
            ]
        )
        
        tagView.configure(with: "7 dayyyyy")
    }
}

class MyViewController : UIViewController {
    override func loadView() {
        let view = UIView()
        view.backgroundColor = .white

        let label = UILabel()
        label.frame = CGRect(x: 150, y: 200, width: 200, height: 20)
        label.text = "Hello World!"
        label.textColor = .black
        
        let myControl = MyControl()
        myControl.translatesAutoresizingMaskIntoConstraints = false
        
        view.addSubview(myControl)
        
        NSLayoutConstraint.activate([
            myControl.centerXAnchor.constraint(equalTo: view.centerXAnchor),
            myControl.centerYAnchor.constraint(equalTo: view.centerYAnchor),
            myControl.widthAnchor.constraint(equalToConstant: 300),
            myControl.heightAnchor.constraint(equalToConstant: 50),
        ])
        
        view.addSubview(label)
        self.view = view
    }
}
// Present the view controller in the Live View window
PlaygroundPage.current.liveView = MyViewController()

内容的提问来源于stack exchange，提问作者Evgenii Shishko