Java Swing: JLabel´s Text / Font shown incompletely

Question

I want to show some kind of information in a JTreeTable and start off with a JDialog, where something is written in JLabels (i think, that's the more unimportant fact).

The problem is, that my JLabel is not shown correctly, there are missing some details (see picture).

I already tried out three kinds of solution:

1.) Working with Runnable,.setLookAndFeel, and .invokeLater:

public NoDataWarningView() {
    Runnable gui = new Runnable() {

        public void run() {
            try {
                UIManager.setLookAndFeel(UIManager
                        .getSystemLookAndFeelClassName());
            } catch (Exception e) {
                e.printStackTrace();
            }
            JOptionPane.showMessageDialog(null,
                    "Some kind of text or information.",
                    "Warning",                        
                        JOptionPane.WARNING_MESSAGE);

        }
    };
    SwingUtilities.invokeLater(gui);
}

2.) Renew the font, before the text is written. It works, but the "OK!" from the button is still missing. Referenced Question

public static void setUIFont (javax.swing.plaf.FontUIResource f){
    java.util.Enumeration keys = UIManager.getDefaults().keys();
    while (keys.hasMoreElements()) {
      Object key = keys.nextElement();
      Object value = UIManager.get (key);
      if (value != null && value instanceof javax.swing.plaf.FontUIResource)
        UIManager.put (key, f);
      }
} 

3. Deleted a Font-File, because it seems, Java-Fonts were corrupt with Windows-Fonts and restarted. Had no effect. Referenced Question

To rebuild the cache: as administrator, delete this file and reboot the PC:

del %WINDIR%\System32\FNTCACHE.DAT

Somebody has a clue concerning the solution?