I have created a form and put the following in additional settings (changed for the post)
on_sent_ok: "location = 'http://<mywebsite>/<mypage>/';"
When I fill the form in I get different responses depending upon the browser used
firefox 13.01 a successful was sent and redirection successful
IE 9 no action - no messages of any kind and no redirection
IE 8 successful message sent - no redirection