Inviseble catpcha breaks the ajax handling

[t3webman]

I handle my form in a modal window so I need the validation and submission to be handled trough an Ajax request ...

plugin.tx_powermail {
     settings {
         setup {
             misc {
                 ajaxSubmit = 1
             }
         }
     }
 }

this works, but invisibile captcha substitutes the submit button and the setting stops having effect !