[TYPO3-mvc] temporary set does db update?

[Ralph Germershausen]

hi there. i try to fill a select with db objects.

<f:form.select name="spublisher" options="{publisherSelect}"
optionValueField="uid" optionLabelField="title" class="style2"
value="{piVars.spublisher}"/>

my problem is that there is a title and shorttitle
so i try to set shorttitle for title if there is one.
BUT.. this change make his way into the db. i am in a list view.
no update actions. this is the second time i ran into problems with set.
is this a wished behaviour and i am doind something wrong or is a bug?

$publisher = $this->publisherRepository->findAllOrdered();
//prepare shorttitle
$publisherArr = array();
foreach($publisher->toArray() as $key => $value) {
    if(trim($value->getTitlenav()) != '') {
          $value->setTitle($value->getTitlenav());
     }
     array_push($publisherArr, $value);
 }