Menu items disappear from primary menu when I save content

I've done som debugging and have found at that it's the menu_node_save()-function that calls the menu_link_delete (line 500 in menu.module). It get's called because $link['enabled'] is empty. $link is set to &$node->menu.

Snippet from function menu_node_save:

/**
 * Helper for hook_node_insert() and hook_node_update().
 */
function menu_node_save($node) {
  if (isset($node->menu)) {
    $link = &$node->menu;
    if (empty($link['enabled'])) {
      if (!empty($link['mlid'])) {
        menu_link_delete($link['mlid']);
      }

Here is a var_dump of $node->menu:

array
  'menu_name' => string 'primary-links' (length=13)
  'mlid' => string '124' (length=3)
  'plid' => string '0' (length=1)
  'link_path' => string 'node/1' (length=6)
  'router_path' => string 'node/%' (length=6)
  'link_title' => string 'Vanliga frågor' (length=15)
  'options' => 
    array
      'attributes' => 
        array
          'title' => string 'Vanliga frågor om luftvärmepumpar' (length=35)
  'module' => string 'menu' (length=4)
  'hidden' => string '0' (length=1)
  'external' => string '0' (length=1)
  'has_children' => string '0' (length=1)
  'expanded' => string '0' (length=1)
  'weight' => string '-48' (length=3)
  'depth' => string '1' (length=1)
  'customized' => string '1' (length=1)
  'p1' => string '124' (length=3)
  'p2' => string '0' (length=1)
  'p3' => string '0' (length=1)
  'p4' => string '0' (length=1)
  'p5' => string '0' (length=1)
  'p6' => string '0' (length=1)
  'p7' => string '0' (length=1)
  'p8' => string '0' (length=1)
  'p9' => string '0' (length=1)
  'updated' => string '0' (length=1)
  'path' => string 'node/%' (length=6)
  'load_functions' => 
    array
      1 => string 'node_load' (length=9)
  'to_arg_functions' => string '' (length=0)
  'access_callback' => string 'node_access' (length=11)
  'access_arguments' => string 'a:2:{i:0;s:4:"view";i:1;i:1;}' (length=29)
  'page_callback' => string 'node_page_view' (length=14)
  'page_arguments' => string 'a:1:{i:0;i:1;}' (length=14)
  'fit' => string '2' (length=1)
  'number_parts' => string '2' (length=1)
  'tab_parent' => string '' (length=0)
  'tab_root' => string 'node/%' (length=6)
  'title' => string 'Vanliga frågor' (length=15)
  'title_callback' => string 'node_page_title' (length=15)
  'title_arguments' => string 'a:1:{i:0;i:1;}' (length=14)
  'type' => string '6' (length=1)
  'description' => string '' (length=0)
  'position' => string '' (length=0)
  'include_file' => string '' (length=0)
  'delivery_callback' => string '' (length=0)
  'context' => string '0' (length=1)
  'theme_callback' => string '' (length=0)
  'theme_arguments' => string 'a:0:{}' (length=6)
  'link_weight' => string '-48' (length=3)
  'href' => string 'node/1' (length=6)
  'access' => boolean true
  'localized_options' => 
    array
      'attributes' => 
        array
          'title' => string 'Vanliga frågor om luftvärmepumpar' (length=35)
  'parent_depth_limit' => int 8

What is $link['enabled'] on how come it's not set?