gform_confirmation filter + ajax = stuck

This is the same issue as reported here:
http://www.gravityhelp.com/forums/topic/gform_confirmation-stuck-issue

I have a small ajax (multi-page) form. After submit I want to do some post-processing of entered values. Depending on this I want to send a custom confirmation message.

Problem: With ajax turned on, the form gets stuck with the ajax spinner image spinning next to the submit button.
The same 'solution' as in previous mentioned forum topic works here: turn ajax off. But that's not a solution! The previous topic was closed as if it was solved, but the real problem still exists. Please provide a real solution.

I used a (simplified) version of the documentation example code:
add_filter("gform_confirmation_7", "custom_confirmation", 10, 4);
function custom_confirmation($confirmation, $form, $lead, $ajax){

$confirmation = array("redirect" =>"http://www.google.com");

return $confirmation;
}