fix-1842516.php

<?php
function field_collection_remove_submit($form, &$form_state) {
  $button = $form_state['triggering_element'];
  $delta = $button['#delta'];

  // Where in the form we'll find the parent element.
  $address = array_slice($button['#array_parents'], 0, -2);

  // Go one level up in the form, to the widgets container.
  $parent_element = drupal_array_get_nested_value($form, $address);
  $field_name = $parent_element['#field_name'];
  $langcode = $parent_element['#language'];
  $parents = $parent_element['#field_parents'];

  $field_state  = field_form_get_state($parents, $field_name, $langcode, $form_state);
  $_field_state = drupal_array_get_nested_value($form_state['field']['#parents'], $address);

  // Go ahead and renumber everything from our delta to the last
  // item down one. This will overwrite the item being removed.
  for ($i = $delta; $i < $field_state['items_count']; $i++) {
    $old_element_address = array_merge($address, array($i + 1));
    $new_element_address = array_merge($address, array($i));

    $moving_element = drupal_array_get_nested_value($form, $old_element_address);
    $moving_element_value = drupal_array_get_nested_value($form_state['values'], $old_element_address);
    $moving_element_input = drupal_array_get_nested_value($form_state['input'], $old_element_address);

    // Tell the element where it's being moved to.
    $moving_element['#parents'] = $new_element_address;

    // Move the element around.
    form_set_value($moving_element, $moving_element_value, $form_state);
    drupal_array_set_nested_value($form_state['input'], $moving_element['#parents'], $moving_element_input);

    // Move the entity in our saved state.
    if (isset($field_state['entity'][$i + 1])) {
      $field_state['entity'][$i] = $field_state['entity'][$i + 1];
      $_field_state[$i] = $_field_state[$i + 1];
    }
    else {
      unset($field_state['entity'][$i]);
      unset($_field_state[$i]);
    }
  }

  // Replace the deleted entity with an empty one. This helps to ensure that
  // trying to add a new entity won't ressurect a deleted entity from the
  // trash bin.
  $count = count($field_state['entity']);
  $field_state['entity'][$count] = entity_create('field_collection_item', array('field_name' => $field_name));

  // Then remove the last item. But we must not go negative.
  if ($field_state['items_count'] > 0) {
    $field_state['items_count']--;
  }

  // Fix the weights. Field UI lets the weights be in a range of
  // (-1 * item_count) to (item_count). This means that when we remove one,
  // the range shrinks; weights outside of that range then get set to
  // the first item in the select by the browser, floating them to the top.
  // We use a brute force method because we lost weights on both ends
  // and if the user has moved things around, we have to cascade because
  // if I have items weight weights 3 and 4, and I change 4 to 3 but leave
  // the 3, the order of the two 3s now is undefined and may not match what
  // the user had selected.
  $input = drupal_array_get_nested_value($form_state['input'], $address);
  // Sort by weight
  uasort($input, '_field_sort_items_helper');

  // Reweight everything in the correct order.
  $weight = -1 * $field_state['items_count'];
  foreach ($input as $key => $item) {
    if ($item) {
      $input[$key]['_weight'] = $weight++;
    }
  }

  foreach ($field_state['entity'] as $i => $info) {
    if (!$info->item_id) {
      unset($field_state['entity'][$i]);
      unset($_field_state['entity'][$i]);
    }
  }

  drupal_array_set_nested_value($form_state['input'], $address, $input);
  drupal_array_set_nested_value($form_state['field']['#parents'], $address, $_field_state);

  field_form_set_state($parents, $field_name, $langcode, $form_state, $field_state);

  $form_state['rebuild'] = TRUE;
}