FULL PRODUCT VERSION :
java version "9"
Java(TM) SE Runtime Environment (build 9+181)
Java HotSpot(TM) 64-Bit Server VM (build 9+181, mixed mode)

ADDITIONAL OS VERSION INFORMATION :
Microsoft Windows [Version 10.0.15063]

EXTRA RELEVANT SYSTEM CONFIGURATION :
system display scaling is set to 200%

A DESCRIPTION OF THE PROBLEM :
When attempting to set a shaped/translucent window via Frame#setBackground, HiDPI mode becomes disabled for most/all Swing component.

Frame#setOpacity appears to work correctly.

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
Run example application listed below on a HiDPI display. Comment out #setBackground call to see expected scaling.

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
Swing components are scaled according to Windows settings.
ACTUAL -
Swing components are not scaled.

REPRODUCIBILITY :
This bug can be reproduced always.

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

public class Main {

public static void main(String[] args) throws Exception {
    JFrame frame = new JFrame("HiDPI test");
    JPanel panel = new JPanel(new GridLayout(2, 0));
    panel.add(new JLabel("Some text"));
    panel.add(new JButton("A button"));
    frame.setContentPane(panel);

    frame.setDefaultCloseOperation(WindowConstants.DISPOSE_ON_CLOSE);
    frame.setUndecorated(true);
    frame.setBackground(new Color(0, 0, 0, .5f)); // this line disabled HiDPI
    // frame.setOpacity(.5f);
    frame.pack();
    frame.setVisible(true);
}

}
---------- END SOURCE ----------