refer to the fiddle sample code

http://zkfiddle.org/sample/3ala753/1-Workaround-for-changing-UUID#source-3

The TestListbox.java need to reset the context menu by
if( resetContext) {
// COMMENT THIS OUT AND RUN IN ZK 6 AND THE CONTEXT MENU WILL NOT WORK.
// IT WILL WORK FINE IN ZK 5 WITHOUT THIS LINE
setContext(popup);
}

This is casue by from ZK 6, the uuid will be different when component is not attached to page, refer to the AbstractComponent.java getUuid() method.

The git log mention the reason of the implementation

• Use z__i for detached components if getUuid is called
  Reason: easy to know what happens