Hi Anette,
Thanks for bringing this to my attention. It is a bug. In mojoPortal the friendly urls are produced with url rewriting so an url like http://mysite.com/home.aspx really maps to the real url http://mysite.com/Default.aspx?pageid=x where the x is a placeholder for the page id. It seems that in the html feature it was using the real url instead of the friendly url. I have just fixed this in my local copy so it will be fixed in the next release of mojoPortal.
In the meantime the only workaround I can think of is to view the source of the page and copy the iframe code. Then disable it from the Html settings and paste the iframe in the editor in html source view, then you can modify the url.
Best,
Joe