I thought browsers would refuse to sumbit to a http url when on a https page without some warning?
Never tried to submit, so never got to see if something happened. Might be able to set up a test to see, won't be trying to pay through the form with an invalid card ;)
Edit: I see that the first part of the process to pay the fees also does the same thing. Never got a warning (other than the greyed out https) in Chrome.