NSSavePanel accessory view disabled in macOS 11 Big Sur

Question

• I create a new macOS app in XCode.

• I add the entitlement com.apple.security.files.user-selected.read-write with value YES (to allow usage of NSSavePanel)

• In AppDelegate.m, I implement applicationDidFinishLaunching as follows:

  - (void)applicationDidFinishLaunching:(NSNotification *)aNotification {
    NSSavePanel* nssavepanel = [NSSavePanel savePanel];
    NSButton* nsbutton = [[NSButton alloc] initWithFrame:NSMakeRect(0, 0, 50, 20)];
    [nsbutton setTitle:@"Button title"];
    [nssavepanel setAccessoryView:[[NSView alloc] initWithFrame:NSMakeRect(0, 0, 200, 80)]];
    [[nssavepanel accessoryView] addSubview:nsbutton];
    [nssavepanel beginWithCompletionHandler:^(NSModalResponse result) {}];
  }
  

When I start the application, I see a panel with a button.

On macOS 10.15.3, I can click the button in the acceessory view.

On macOS 11.0 Beta (20A4300b), I cannot click the button -- the whole accessory view seems to be disabled. (If I use runModal or beginSheetModalForWindow instead of beginWithCompletionHandler, the accessory view works as expected.) Is this a bug? Am I doing something wrong here?