That's because it isn't done in the whizzywig code, it's done by the browser itself: Internet Explorer always does this ut Firefox tends to leave your links alone.

For a project I have been working on I wanted to implement this fine application, but I have been having troubles modifying the code so relative paths for images and links are not replaced by the full path.  I can't find where in the code where the "/somefolder/somefile" is replaced with http://yoursite/somefolder/somefile.