The dragging of decorated frames is buggy and jumpy. Probably due to MetalRootPaneUI.MetalTitlePane.mouseDragged not working the way it should be.

//Testcase
import javax.swing.*;
public class FrameDemo extends JFrame {
  public FrameDemo(){
    setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    setSize(200,200);
    setVisible(true);
  }
  public static void main(String[] args){
    JFrame.setDefaultLookAndFeelDecorated(true);
    new FrameDemo();
  }
}