formtastic - multiple forms with check boxes leads to double used html id

Problem: When creating muliple, similar structured forms with formtastic and using check boxes, then all the forms seems to be correlated: Checking a check_box of the check_boxes in one form, changes them in another, too. This is because they all used the same id for the check box input. One can change this, by using the option index => object.id in the semantic form for:

semantic_form_for user, :index => user.id do |f|
 ....
  f.input :options, :as => :check_boxes
end

In this way, the checkboxes get a prefix of the given index. This option seems to be undocument, but can be found in the source code choice_input_dom_id.

Reposted from notes.it-jobs-und-stellen.de