Bug 1) I put in <img onmouseover="alert('hi')" src="http://cutesoft.net/Themes/default/images/common/title.gif"> via HTML mode in the test URL
http://richtextbox.net/test/ and click show HTML, it does not get stripped out and I get an alert when mousing over the image.
Bug 2) Also tested to make sure script tags still get stripped out and I get a .NET runtime error error on your site
http://richtextbox.net/test/ when clicking show HTML with the following inputed in HTML mode <script>alert('crashforums')</script>
Server Error in '/' Application.
Runtime Error
Not sure if you have EnableStripScriptTags set to false? I know by default it is set to true.
Jason