Save and preview differences in hook_form_alter()
First, you should use #access = FALSE which will disallow access to a element. #type hidden is not safe, it means that it is printed as a hidden input field which can be easily changed by the user, for example with Firebug.

When you do that, you can also directly set #access on the field element, like $form['field_versio']['#access'] and it will disallow access to all subelements (if there are multiple).

Not sure why it doesn't work in Preview, try adding a drupal_set_message('test') call to see if your hook is called.