[TYPO3-mvc] Controller $this->forward with arguments - does not work?

[Tim Schoch | GSTALTIG]

Hello List

I'm failing at a simple task:
In my app I wan't to forward from one controller action to another by passing an argument.
----------------------------
/* @param Item $item */
controller->entryAction( Item $item ) {
    switch( $item->getType() ) {
      case 'foo':
        $this->forward( 'foo', NULL, NULL, array( 'item' => $item ) );
        break;
      case 'bar':
        $this->forward( 'bar', NULL, NULL, array( 'item' => $item ) );
        break;
      ...
    }
  }
(Code shortened)
----------------------------

Problem is, I always get this Error:
----------------------------
An error occurred while trying to call Tx_Myext_Controller_ITemController->fooAction().
Error:   Required property 'item' does not exist.  
----------------------------
But the $item must be totaly fine, as it has already passed the validation as the entryAction was called.
How is it supposed to be done?

Thanks in advance
Tim