ArcObjects Add-in closes ArcMap when JFrame is closed

Question

My Add-in opens a new frame for user input. When this frame is closed, ArcMap also closes. I have the DefaultCloseOperation set to DISPOSE_ON_CLOSE.

My code inside the add-in button creates an instance of my GUI class.

public void onClick() throws IOException, AutomationException {
    SwingUtilities.invokeLater(new Runnable() {
        public void run() {
            createGUI();
        }
    });

Any Ideas? I want the user to be able to exit the window normally and continue working in ArcMap.