Java.awt Robot createScreenCapture() fail to capture any popup dialog

FULL PRODUCT VERSION :
java version "1.8.0_101"
Java(TM) SE Runtime Environment (build 1.8.0_101-b13)
Java HotSpot(TM) 64-Bit Server VM (build 25.101-b13, mixed mode)

ADDITIONAL OS VERSION INFORMATION :
ubuntu 15.04 +
fedora 22+


A DESCRIPTION OF THE PROBLEM :
Java awt Robot createScreenCapture() fail to capture any popup dialog box on *nix distro,

The captured image will only contains the frame of the dialog box, but the content of the dialog box is virtually transparent.



STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
1. Open Firefox
2. Open the about dialog box
3. capture screen shot using awt Robot

similarily, open Eclipse IDE, open preference windows, capture screenshot

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
Screen image is saved.
Image should contains all visible UI elements on screen
ACTUAL -
the dialog box on the image is transparent
the terminal windows border is removed

REPRODUCIBILITY :
This bug can be reproduced always.

---------- BEGIN SOURCE ----------
    public static void main(String[] args) {
        try {
            Thread.sleep(3000); // wait 3 seconds
            Robot robot = new Robot();
            String format = "jpg";
            String fileName = "FullScreenshot." + format;
            
            Rectangle screenRect = new Rectangle(Toolkit.getDefaultToolkit().getScreenSize());
            BufferedImage screenFullImage = robot.createScreenCapture(screenRect);
            ImageIO.write(screenFullImage, format, new File(fileName));
            
            System.out.println("A full screenshot saved!");
        } catch (Exception ex) {
            System.err.println(ex);
        }
    }
---------- END SOURCE ----------

CUSTOMER SUBMITTED WORKAROUND :
NONE ..