Message1709

JComboBox has a method actionPerformed since it implements ActionListener.  A method is higher in the visibility ordering than a bean event property, so it's taking precedence and coming back for actionPerformed as explained on http://jython.org/Project/userguide.html#methods-properties-and-event-properties.  Jython is complaining that it can't assign your method on top of the existing JComboBox actionPerformed method.  

You can get around this by using the more cumbersome addActionListener method.  Create a Python class that implements ActionListener, put your select_jc_item method in it as "actionPerformed" and call jc.addActionListener with an instance of your ActionListener subclass.

In the future, send stuff where you're not sure if it's a bug or not to jython-users. Many more people monitor it so you have a better chance at a timely response, and answers there turn up more readily in search results than the bug database.