[TYPO3-mvc] after upgrade 6.0 to 6.1 error with domain model update "must be persisted already, but is new"

[Domi]

Hello,

I struggle with an extension updated vom TYPO3 6.0 to 6.1

In 6.0 it worked without problem:

My form:
     <f:form method="post" name="client" object="{client}" 
action="intranetStep1Save" class="form-horizontal" noCache="true">
  (...)
</f:form>


My save action:
/**
  * intranetStep1SaveAction
  *
  * @param $client
  *
  * @return void
*/
public function 
intranetStep1SaveAction(\DMF\Intranet\Domain\Model\Client $client) {
	$this->clientRepository->update($client);
	$this->redirect('intranetStep2View');
}

Now I receive following error:

#1249479819: The object of type "DMF\Intranet\Domain\Model\Client" given 
to update must be persisted already, but is new.

There must be a breaking change from 6.0 to 6.1, can somebody help me 
out? If I debug, my $client is a valid object of the Client model.

This might relate to the fact, that I try to do partial validation?

Thanks for help,
Dominic