FULL PRODUCT VERSION :
java version "1.8.0_25"
Java(TM) SE Runtime Environment (build 1.8.0_25-b17)
Java HotSpot(TM) 64-Bit Server VM (build 25.25-b02, mixed mode)


ADDITIONAL OS VERSION INFORMATION :
Mac OS X 10.8.5, Mac OS X 10.9.5

A DESCRIPTION OF THE PROBLEM :
The example code should render the two characters combinded. The problem occurs only on Mac OS X with Oracle Java 7,8 and with Apple Java 6u65.

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
Launch the example code on Mac OS X and another OS (Windows 7 or Linux). Compare the rendered results in the text field.

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
Display of combined characters.
ACTUAL -
The charcters are not combinded.The mark space combining character is rendered "standalone" showing the placeholder dotted circle.

REPRODUCIBILITY :
This bug can be reproduced always.

---------- BEGIN SOURCE ----------
import java.awt.Font;

import javax.swing.JFrame;
import javax.swing.JTextField;
import javax.swing.SwingUtilities;

public class MarkSpacingCombiningTest extends JTextField{

// Unicode Character 'KHMER LETTER TA' (U+178F)
// Category Letter, Other [Lo]
// http://www.fileformat.info/info/unicode/char/178f/index.htm
// and
// Unicode Character 'KHMER VOWEL SIGN OE' (U+17BE)
// Category Mark, Spacing Combining [Mc]
// http://www.fileformat.info/info/unicode/char/17be/index.htm
//
private String exampleText="\u178F\u17BE";


    public MarkSpacingCombiningTest() {
       super();
    }
    
    protected void setExampleText() {
        Font f=getFont().deriveFont((float)80.0);
        if(f.canDisplayUpTo(exampleText)!=-1){
         // Set "Khmer UI" font on Windows 7
         f=new Font("Khmer UI",Font.PLAIN,80);
         System.out.println("Using font family Khmer UI");
        }
        setFont(f);
        setText(exampleText);
        repaint();
    }

    public static void main(String[] args) {
        final MarkSpacingCombiningTest t=new MarkSpacingCombiningTest();
        System.out.println("Java version: "+System.getProperty("java.vendor")+" "+System.getProperty("java.version"));
        Runnable sr=new Runnable() {
            @Override
            public void run() {
                JFrame f =new JFrame();
                f.getContentPane().add(t);
                t.setExampleText();
                f.pack();
                f.setVisible(true);
                f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                f.repaint();
            }
        };
        SwingUtilities.invokeLater(sr);
    }
}

---------- END SOURCE ----------