Steps to reproduce:

1. create API request:

   1. API::Action()->get([
          'output' => ['actionid', 'name'],
          'selectAcknowledgeOperations' => ['operationid', 'recovery'],
          'actionids' => 3
      ]);

Result:

1. incorrect response:

   Array
   (
       [0] => Array
           (
               [actionid] => 3
               [name] => Report problems to Zabbix administrators
               [acknowledgeOperations] => Array
                   (
                   )
           )
       [1] => Array
           (
               [acknowledgeOperations] => Array
                   (
                       [0] => Array
                           (
                               [operationid] => 12
                               [recovery] => 2
                           )
                   )
           )
   )

2. Error message:

   Undefined index: actionid [hostgroups.php:65 ? CApiWrapper->__call() ? CFrontendApiWrapper->callMethod() ? CApiWrapper->callMethod() ? CFrontendApiWrapper->callClientMethod() ? CLocalApiClient->callMethod() ? CAction->get() ? CAction->addRelatedObjects() in include/classes/api/services/CAction.php:2043]