FULL PRODUCT VERSION :
java version "1.7.0-ea"
Java(TM) SE Runtime Environment (build 1.7.0-ea-b03)
Java HotSpot(TM) Client VM (build 1.7.0-ea-b03, mixed mode, sharing)

A DESCRIPTION OF THE PROBLEM :
If the method JRootPane.setDefaultButton is used to define a default button then that button is triggered if the user press the enter key while focusing another button. This is not a direct violation of method spec. but one may assume that the focused button is triggered when enter key is pressed. For instance; if a JTextField is selected, then the current behavior is the correct one.

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
Attach two buttons to a frame, make one button the default button, use tab-button to focus the other button. Press enter. The unfocused/default button is triggered.

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
The focused JButton should consume the key event. (similar to how a JTextArea consumes enter key events).
ACTUAL -
The unfocused/default JButton is triggered.

REPRODUCIBILITY :
This bug can be reproduced always.

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

public class Test5
{
public static void main(String ... args)
{
JButton ok = new JButton("OK");
JButton cancel = new JButton("Cancel");

ok.addActionListener(new ActionListener()
{
public void actionPerformed(ActionEvent aEvent)
{
System.out.println("ok pressed");
}
});

cancel.addActionListener(new ActionListener()
{
public void actionPerformed(ActionEvent aEvent)
{
System.out.println("cancel pressed");
}
});

JPanel panel = new JPanel(new BorderLayout());
panel.add(cancel,BorderLayout.WEST);
panel.add(ok,BorderLayout.EAST);

JFrame f = new JFrame();
f.add(new JTextField(60), BorderLayout.CENTER);
f.add(panel, BorderLayout.SOUTH);
f.pack();
f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
f.getRootPane().setDefaultButton(ok);
f.setVisible(true);
}
}
---------- END SOURCE ----------

CUSTOMER SUBMITTED WORKAROUND :
Do not use JRootPane.setDefaultButton ...