Sidebar created on macOS 26 with NSSplitViewItem(sidebarWithViewController:) is cut off at the top in fullscreen mode

I noticed that when I have a fullscreen window in macOS 26, sidebars look like they are cut off at the top: they suddenly stop where the title bar/toolbar would appear when moving the mouse to the top of the screen, leaving a wide empty gap. Am I the only one who finds this ugly? Is this intended, or is there a workaround?

This is how it looks in fullscreen (the sidebar borders are not easy to distinguish, look for the drop shadow):

And this when moving the mouse to the top screen border to show the menu bar:

I created FB20291636.

@main
class AppDelegate: NSObject, NSApplicationDelegate, NSWindowDelegate {

    func applicationDidFinishLaunching(_ aNotification: Notification) {
        let splitViewController = NSSplitViewController()
        splitViewController.addSplitViewItem(NSSplitViewItem(sidebarWithViewController: ViewController()))
        splitViewController.addSplitViewItem(NSSplitViewItem(viewController: ViewController()))
        let window = NSWindow(contentViewController: splitViewController)
        window.styleMask = [.titled, .closable, .miniaturizable, .resizable, .fullSizeContentView]
        window.toolbar = NSToolbar()
        window.delegate = self
        window.makeKeyAndOrderFront(nil)
    }

    func window(_ window: NSWindow, willUseFullScreenPresentationOptions proposedOptions: NSApplication.PresentationOptions = []) -> NSApplication.PresentationOptions {
        return [.autoHideToolbar, .autoHideMenuBar, .fullScreen]
    }

}

class ViewController: NSViewController {

    override func loadView() {
        let stack = NSStackView(views: [
            NSTextField(labelWithString: "asdf")
        ])
        stack.orientation = .vertical
        stack.alignment = .leading
        view = stack
        view.frame = CGRect(x: 0, y: 0, width: 300, height: 300)
    }

}