I have sent you an email containing a test account to use on our server.  Mind you that v4.X worked fine with the same code under Firefox and Netscape.  This version breaks Netscape AND Firefox, but works in IE.

 

The strange thing is that doing an alert(editor.GetHTML()); on button click before postback reveals the content is correct.  Putting a break on Page_Load shows that the content reverted back to the previous state.