Undo (Ctrl+Z) and Redo (Ctrl+Y) actions don't work in the HTML Editor in the "Advanced Form" example on IE, Safari and Chrome. They do work on Firefox and Opera.
I got to this because in my application I use GWT's RichTextArea with GXT components and undo and redo don't work only in Chrome and Safari after the RichTextArea looses focus and regains focus. undo and redo work fine on Chrome and Safari in a simple test application. I use GWT 2.1.0 and GXT 2.2.1. I am still investigating this problem, not sure if it's related to the problem in the GXT HtmlEditor.