I don't know if it makes a difference, but I am using NetBeans and it is adding the toolbar to the desktop:
org.jdesktop.layout.GroupLayout layout = new org.jdesktop.layout.GroupLayout(getContentPane());
getContentPane().setLayout(layout);
layout.setHorizontalGroup(
layout.createParallelGroup(org.jdesktop.layout.GroupLayout.LEADING)
.add(desktopPane, org.jdesktop.layout.GroupLayout.DEFAULT_SIZE, 1142, Short.MAX_VALUE)
);
layout.setVerticalGroup(
layout.createParallelGroup(org.jdesktop.layout.GroupLayout.LEADING)
.add(desktopPane, org.jdesktop.layout.GroupLayout.DEFAULT_SIZE, 745, Short.MAX_VALUE)
);
java.awt.Dimension screenSize = java.awt.Toolkit.getDefaultToolkit().getScreenSize();
setBounds((screenSize.width-1150)/2, (screenSize.height-800)/2, 1150, 800);
If i have the toolbar added to the JFrame, then the combo boxes do not all display and they do not work. Whenever the user makes a different selection in the combo boxes on the toolbar, the JInternal frame changes it's data.