Steps to Reproduce

http://zkfiddle.org/sample/32ovgu2/1-ckeditor-memory-leak
Click the add editor button
Wait until the editor flickers in and out

Current Result

unbind doesn't clear editor
An unbound editor exist in JavaScript memory (can be found with zk.$('@ckeditor'))
clicking the popup button cause NPE due to unbound editor zWatch listener for Vparent

Expected Result

Editor should be cleaned up during unbind

Debug Info

https://github.com/zkoss/zkckeditor/blob/master/ckez/src/archive/web/js/ckez/CKeditor.js#L160
If the instance._editor field is null, the unbind method will go in the first if condition and will stop at:
https://github.com/zkoss/zkckeditor/blob/master/ckez/src/archive/web/js/ckez/CKeditor.js#L163

This can be caused by removing an editor instance before it is fully initialized

Root Cause

https://sourceforge.net/p/zk1/bugs/2205/

Workaround