FULL PRODUCT VERSION :
java version "1.8.0_51"
Java(TM) SE Runtime Environment (build 1.8.0_51-b16)
Java HotSpot(TM) 64-Bit Server VM (build 25.51-b03, mixed mode)

ADDITIONAL OS VERSION INFORMATION :
OS X 10.10.5

A DESCRIPTION OF THE PROBLEM :
On OS X, an editable JComboBox with custom editor does not respond to up/down arrow keys.
If the default editor is used, the drop down list is navigable using the up / down arrow keys.
If another editor is used (e.g. javax.swing.plaf.basic.BasicComboBoxEditor) then keys are ignored.

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
Create an editable combobox with some items and set a custom combobox editor.
Run the supplied app. One combobox sets an editor the other uses the default - only the default will work.

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
Both comboboxes should allow selection of items with up down arrow.
ACTUAL -
The default editor will function as expected (allows selection of items with up down arrow).
The custom editor will not respond to arrows.

REPRODUCIBILITY :
This bug can be reproduced always.

---------- BEGIN SOURCE ----------
import javax.swing.ComboBoxEditor;
import javax.swing.JComboBox;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
 
public class ComboBoxTest
{
    private static void createAndShowGUI()
    {
        JPanel panel = new JPanel();
        
        // create an editable JComboBox with a ComboBoxEditor
        JComboBox cb1 = new JComboBox();
        cb1.setEditable(true);
        ComboBoxEditor cbe1 = new javax.swing.plaf.basic.BasicComboBoxEditor();
        System.out.println("No arrow selection combo: ComboBoxEditor == " + cbe1);
        cb1.setEditor(cbe1);
        
        cb1.addItem("test1");
        cb1.addItem("test2");
        cb1.addItem("test3");
 
        panel.add(new JLabel("No arrow selection combo:"));
        panel.add(cb1);
                
        // create an editable JComboBox using default ComboBoxEditor
        JComboBox cb2 = new JComboBox();
        cb2.setEditable(true);
        ComboBoxEditor cbe2 = cb2.getEditor();
        System.out.println("Arrow selection works: ComboBoxEditor == " + cbe2);
        //cb2.setEditor(cbe2);
        
        cb2.addItem("test1");
        cb2.addItem("test2");
        cb2.addItem("test3");
        
        panel.add(new JLabel("Arrow selection works:"));
        panel.add(cb2);
 
        JFrame frame = new JFrame();
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.getContentPane().add(panel);
        frame.pack();
        frame.setVisible(true);
    }
    
    public static void main(String[] args)
    {
        javax.swing.SwingUtilities.invokeLater(new Runnable()
        {
            @Override
            public void run()
            {
                createAndShowGUI();
            }
        });
    }
}

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