SystemEventQueueUtilities.RunnableCanvas is getting focus, causing keyboard bindings to now work.
Try running the following program and selecting test->test from the menu. This will create a new InternalFrame. On the console it will print out the current focus owner, which becomes the RunnableCanvas. Since the RunnableCanvas has focus the binding control-n will not work. If you click on the button the button will get focus and control-n will work again. Closing the internal frame causes focus to go back to the RunnableCanvas, and bindings won't work again.
import com.sun.java.swing.*;
import java.awt.*;
import java.awt.event.*;

public class IFTest {
    Runnable focusRunnable;

    public IFTest() {
JMenuBar mb = new JMenuBar();
JMenu menu = new JMenu("Test");
JMenuItem newMI = new JMenuItem("test");
final JFrame frame = new JFrame("TEST");
final JDesktopPane dp = new JDesktopPane();

mb.add(menu);
menu.add(newMI);
frame.setJMenuBar(mb);
dp.setPreferredSize(new Dimension(400, 400));
newMI.setAccelerator(KeyStroke.getKeyStroke(KeyEvent.VK_N,
InputEvent.CTRL_MASK));
focusRunnable = new Runnable() {
public void run() {
System.out.println("Focus Owner: " + frame.getFocusOwner());
}
};
newMI.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent ae) {
JInternalFrame jif = new JInternalFrame("IF");
JTextField tf = new JTextField("HI");

jif.getContentPane().add(new JButton("HI"));
jif.setBounds(10, 10, 200, 200);
jif.setClosable(true);
dp.add(jif, 5);
System.out.println("NEW");
SwingUtilities.invokeLater(focusRunnable);
}
});

frame.getContentPane().add(dp, BorderLayout.CENTER);
frame.pack();
frame.show();
SwingUtilities.invokeLater(focusRunnable);
    }

    public static void main(String[] args) {
new IFTest();
    }
}
It should be noted this only happens on Solaris, NT doesn't seem to have this behavior.