The official way of creating a button is defined by the base theme. in short, it should be this way:
$qa_content['q_view']['form']['buttons']['button-id'] = array(
'tags' => 'name="a-name"',
'label' => 'A label',
'popup' => 'A title',
You might complain and say SnowFlat doesn't show the label. That's true, because this theme expects buttons to be images. You can turn your button to contain text by just applying some CSS to it:
padding: 0 10px;
Now, if you need to pass a post ID, you can use a hidden field in the form. Or even better, just: qa_request_part(0), after making sure the qa_clicked('button-id') is the one you expected.