Multiple Field , same ajax callback

I created a custom field. The hook_field_widget_form has an submit element with an ajax callback:

  //Add more   $  element['add_zone'] = array(     '#type' => 'submit',     '#name' => $  field_name . '-add_more-' .'name',     '#value' => t('+'),     '#limit_validation_errors' => array(),     '#submit' => array('dms_polygone_add_more_add_one'),     '#ajax' => array(       'callback' => 'dms_polygone_add_more_callback',       'wrapper' => 'zones-fieldset-wrapper-'. $  field_name,     ),   ); 

I add 2 fields of my custom field type to a node. Ex: field_polygone (field type: polygone) and field_polygone_2 (field type: polygone). When i press the ‘add_more’ button of my first field_polygone, my callback function ‘dms_polygone_add_more_add_one’ thinks the trigger element is field_polygone_2.

Callback function:

function dms_polygone_add_more_callback($  form, $  form_state) {   //@todo: $  i gebruiken voor veld als er meerdere waardes zijn toegestaan.   $  parents = $  form_state['triggering_element']['#parents'];   return $  form[$  parents[0]][$  parents[1]][$  parents[2]]['zones']; } 

$ parents[0] is het field_name => When the i press ‘add_more’ , the $ parents[0] variable in the callback function should be ‘field_polygone’, but its field ‘field_polygone_2’.

How can is solve this problem? Why does the callback function think the trigger element is field_polygone_2 instead of field_polygone.