It is not supported by the Rich Text Editing engine of the browser to have only an opening <div> or another tag or only a closing </div> tag in the content area. Every HTML tag is a node in the DOM and it should have an opening and closing tag, in other case the content will be invalid HTML/XHTML.
The browser's Rich Text Editing engine checks for unclosed and non well formed tags and corrects or try to correct them automatically without providing a way to disable the browser validation. You can verify my words by testing the attached HTML page with an editable IFRAME element in it. You will reproduce the same behavior with an editable DIV element as well as in our competitors' editors.
the Telerik team
Registration for Q1 2011 What’s New Webinar Week is now open. Mark your calendar for the week starting March 21st and book your seat
for a walk through all the exciting stuff we ship with the new release!