Modal dialog prevents form submission

I am attempting to use a modal dialog to confirm form submission. However if I any attempt to submit the form in the dialog's 'confirm' button event handler fails (nothing happens).

For example, see the attached test case.

I would expect this test case to work, however clicking confirm does nothing, and no errors are raised. Any code inserted into the button handler following the 'submit()' call is executed as expected, so it appears the submit() call is actually called called, it just exits quietly without doing anything.

Other things I've attempted such as using $("#testform").get(0).submit() to call the form's submit method directly also fail.