Importing nodes in bulk fail to create titles for all nodes after the first one

This is due to there not being an $id returned from entity_extract_ids when called, and then the $sync static variable winds up reusing the same location for each consecutive call. I noticed this happening during a Feed import run and tracked it down to the presave hook.

Problem code:

  $sync = &drupal_static(__FUNCTION__, array());
  list($id, , $bundle) = entity_extract_ids($entity_type, $entity);
  $langcode = field_valid_language($langcode, FALSE);

  // We do not need to perform this more than once.
  if (!empty($sync[$entity_type][$id][$langcode][$set])) {
    return;
  }

Fix:

if (!empty($id) && !empty($sync[$entity_type][$id][$langcode][$set])) {

There may possibly be a better alternative to using $id to build this array.