Comment 36 for bug 37330

Any implementation of Java (be it Sun's or the OpenJDK) suffers from this bug. Some Java Applet Windows cannot be closed when clicking on the close button (X) on the Window Manager title bar.

This bug only affects Linux distributions. On MS Windows, the Applets work normally and they can be closed at will as any other window.

Sites where this bug happens:
http://www.chat-avenue.com/
http://www.elchat.com
...and pretty much any Applets that do not have an explicit close function within themselves.