Cocoa FocusRing gets distorted when its view gets resized - cocoa

Question

I display an NSWindow that contains an NSbutton. The button can be focussed with the tab key for keyboard interaction, the standard focus ring is shown around the button.
The window has a fixed aspect ratio and can be resized as a whole. When this happens, all content should resize, i.e. the button gets larger or smaller.
This works fine so far. However, the focus ring does only kind of resize properly: the general position and its width are fine, but its heigth does not match the button’s heigth anymore.
Here is how the window initially looks like:
...and here after the window is resized:
You'll probably notice that the text gets slightly disproportional as well, but to no such extent as the focus ring is misplaced.
What steps do I have to take to have the focus ring match its corresponding button at all zoom levels?
Here is my code:
import Cocoa
#main
class AppDelegate: NSObject, NSApplicationDelegate {
var window: NSWindow!
func applicationDidFinishLaunching(_ aNotification: Notification) {
window.contentViewController = MyViewController(size: NSSize(width: 200, height: 72))
window.minSize = CGSize(width: 200, height: 100)
window.aspectRatio = NSMakeSize(2,1)
}
}
class MyViewController: NSViewController {
public init(size: NSSize) {
super.init(nibName: nil, bundle: nil)
self.view = MyView(frame: NSRect(x: 0, y: 0, width: size.width, height: size.height))
}
required init?(coder: NSCoder) {
fatalError("init(coder:) has not been implemented")
}
}
class MyView: NSView {
let initialFirstResponder: NSView
public override init(frame: NSRect) {
let textField = NSTextField(labelWithString: "Textfield")
textField.isEditable = false
textField.frame = NSRect(x: 20, y: 36, width: 100, height: 15)
let switchButton = NSButton(title: "Switch", target: nil, action: nil)
switchButton.frame = NSRect(x: 100, y: 31, width: 80, height: 20)
self.initialFirstResponder = switchButton
super.init(frame: frame)
self.bounds = frame
self.postsBoundsChangedNotifications = true
NotificationCenter.default.addObserver(forName: NSView.frameDidChangeNotification, object: self, queue: OperationQueue.main, using: {(note) in
self.setBoundsSize(NSSize(width: 200, height: 72)) // 28px for titlebar
print("Frame nun \(self.frame.width) x \(self.frame.height)")
})
self.addSubview(textField)
self.addSubview(switchButton)
self.autoresizesSubviews = true
}
required init?(coder: NSCoder) {
fatalError("init(coder:) has not been implemented")
}
}