Native FileChooser corners not rounded

I have the top corners that are not rounded (because there is like a light grey background at the top) when opening a native fileChooser in a plugin on osx :

 FileChooser fc ("Choose a file...",
                 File::getSpecialLocation (File::userDesktopDirectory),
                 "*", true);

 if (fc.browseForFileToOpen())
 {
    ...
 }

Any idea why/how I could get that!? perhaps an opacity issue?

The native file chooser is designed to be attached on the main window, thats why it has rectangle borders on the top. But its a very bad idea to use in a plugin, because it has modal behavior (the message thread gets wrapped). Some hosts may crash because of this behavior. You can choose the file-choose from juce, and use it an non modal window.

I’m not sure : if you look at the native file browser of the ‘Dialog Boxed’ demo, you’ll see that its corners are rounded there. ?