weird thing happening with JComboBox

[alex earnshaw]

I am using a JComboBox as an editor in a JTable, and am having a problem with the ItemListener. I have the combo set up so that the user has to double click on the cell before the combo will open (using setClickCountToStart method on DefaultCellEditor).
According to the swing tutorial, a JComboBox will fire two itemStateChanged events when a new item is selected in a combo and it will not fire any itemStateChanged events if the same item is selected.
In my combo, when you double click, the combo opens showing the drop down list, when you click again (without moving the mouse) it closes. The selection in the combo is the same as it was before you double clicked. But still the itemStateChanged event is being fired!!!
Can anyone tell me why this happens and/or how to fix it? I only want to do something when the selection actually changes....
Here is a code extract:

  
DefaultCellEditor opEditor = new DefaultCellEditor(opCombo);
opEditor.setClickCountToStart(2);
opCombo.addItemListener(new ItemListener(){
    public void itemStateChanged(ItemEvent e)
    {
//this should work but for some reason the double click 
//used to start the combo is causing a itemStateChanged
//even though the selection isn't changing!
logger.debug("op combo item state changed");
        doSomething();
    }
});  
tableColumn.setCellEditor(opEditor);  

Thanks in advance!
Alex