Cancel button does'nt work in RT editor

Start editing a wiki page in RT editor. Make some modifications, and click "Cancel" button.

Chrome's error console:
Uncaught TypeError: Object #<an Object> has no method 'dispatchEvent' prototype.js:2208
z
_methodized prototype.js:166
XWiki.actionButtons.EditActions.Class.create.notify actionButtons.js:122
XWiki.actionButtons.EditActions.Class.create.onCancel actionButtons.js:80
l prototype.js:146
F prototype.js:2149

Firefox's error console::
element.dispatchEvent is not a function
http://localhost:8080/xwiki/resources/js/prototype/prototype.js
Line 4619