Window title bar in macOS 26 is drawn even if titlebarAppearsTransparent = true

macOS 26 sometimes draws the title bar background even when setting NSWindow.titlebarAppearsTransparent = true and I don't understand the logic behind it, or how I can turn this off.

I'm trying to do something similar to Xcode's "Welcome to Xcode" window which has a left view and a right table view.

In my simplified example, the window contains a label and a text view. This used to work in macOS 15, but in macOS 26 the text view is partially covered by the title bar:

As soon as I remove the line scrollView.hasVerticalScroller = true, the title bar isn't drawn anymore:

The title bar also isn't drawn when removing the view on the left of the text view:

I created FB20341654.

This may be related to this other issue: NSWindow.titlebarAppearsTransparent only works after collapsing and expanding sidebar

@main
class AppDelegate: NSObject, NSApplicationDelegate {

    func applicationDidFinishLaunching(_ aNotification: Notification) {
        let window = NSWindow(contentViewController: ViewController())
        window.titlebarAppearsTransparent = true
        window.titleVisibility = .hidden
        window.styleMask = [.titled, .closable, .fullSizeContentView]
        window.makeKeyAndOrderFront(nil)
    }

}

class ViewController: NSViewController {

    override func loadView() {
        view = NSView(frame: CGRect(x: 0, y: 0, width: 400, height: 200))
        
        let scrollView = NSScrollView()
        scrollView.hasVerticalScroller = true // commenting this line out solves the issue
        scrollView.translatesAutoresizingMaskIntoConstraints = false
        scrollView.automaticallyAdjustsContentInsets = false
        
        let documentView = NSTextView()
        documentView.string = (0..<10).map({ "\($0)" }).joined(separator: "\n")
        scrollView.documentView = documentView
        
        let stack = NSStackView(views: [
            NSTextField(labelWithString: "asdfasdfasdfasdf"), // commenting this line out also solves the issue
            scrollView
        ])
        stack.orientation = .horizontal
        view.addSubview(stack)
        NSLayoutConstraint.activate([stack.topAnchor.constraint(equalTo: view.topAnchor), stack.leadingAnchor.constraint(equalTo: view.leadingAnchor), stack.trailingAnchor.constraint(equalTo: view.trailingAnchor), stack.bottomAnchor.constraint(equalTo: view.bottomAnchor)])
    }

}