FULL PRODUCT VERSION :
java version "9.0.1"
Java(TM) SE Runtime Environment (build 9.0.1+11)
Java HotSpot(TM) 64-Bit Server VM (build 9.0.1+11, mixed mode)

ADDITIONAL OS VERSION INFORMATION :
OS X 10.12.6

A DESCRIPTION OF THE PROBLEM :
Under Java 9, once a JFrame is maximized, any new JFrames that are open default to maximized. This was not the behavior under Java 8 and earlier.

REGRESSION. Last worked in version 8u152

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
Run program on OS X. Maximize the window. Push the button.

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
Expect the new JFrame to open unmaximized.
ACTUAL -
The new JFrame opens maximized.

REPRODUCIBILITY :
This bug can be reproduced always.

---------- BEGIN SOURCE ----------
import javax.swing.*;
import java.awt.event.*;

public class FrameBug {

   public static void main(String[] args) {
      SwingUtilities.invokeLater(
         new Runnable() {
            public void run() {
               go();
            }
         });
   }

   public static void go() {
      final JFrame frame = new JFrame();
      JButton button = new JButton("Open Frame");
      frame.getContentPane().add(button);
      button.addActionListener(
         new ActionListener() {
            public void actionPerformed(ActionEvent e) {
               JFrame f = new JFrame();
               f.setSize(400, 400);
               f.setVisible(true);
            }
         });
      frame.setSize(500, 500);
      frame.setVisible(true);
   }
}
---------- END SOURCE ----------